doc(toolchain): sync spark-connector with master

[bitflicker64]

Purpose of the PR

Sync the hugegraph-spark-connector docs (en + cn) with hugegraph-toolchain master (3b385c3d).

Every row below applies to both content/en/docs/quickstart/toolchain/hugegraph-spark-connector.md and content/cn/docs/quickstart/toolchain/hugegraph-spark-connector.md; the two pages are kept in sync.

Page	What was wrong	What changed	Source on master
content/{en,cn}/docs/quickstart/toolchain/hugegraph-spark-connector.md	Overview did not say that reading is unsupported or which id strategies work	Added a note: the table only implements SupportsWrite; CUSTOMIZE and PRIMARY_KEY supported, AUTOMATIC rejected	hugegraph-spark-connector/src/main/scala/org/apache/hugegraph/spark/connector/HGTable.scala:30, hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/builder/VertexBuilder.java:79
content/{en,cn}/docs/quickstart/toolchain/hugegraph-spark-connector.md	Environment listed a vague "Spark 3.x" and "Scala 2.12"	Pinned to Spark 3.2.2 (provided scope) and Scala 2.12.11	hugegraph-spark-connector/pom.xml:43, hugegraph-spark-connector/pom.xml:44, hugegraph-spark-connector/pom.xml:48
content/{en,cn}/docs/quickstart/toolchain/hugegraph-spark-connector.md	Build section never said what artifact the build produces	Documented the *-jar-with-dependencies.jar output for spark-submit --jars	hugegraph-spark-connector/pom.xml:207, hugegraph-spark-connector/pom.xml:210
content/{en,cn}/docs/quickstart/toolchain/hugegraph-spark-connector.md	Usage did not state that format must be the full class name, nor how to pass auth	Added a sentence on the full class name (no DataSourceRegister service file under src/main/resources) and on username / token options	hugegraph-spark-connector/src/test/scala/org/apache/hugegraph/spark/connector/SinkExampleTest.scala:59, hugegraph-spark-connector/src/test/scala/org/apache/hugegraph/spark/connector/SinkExampleTest.scala:82
content/{en,cn}/docs/quickstart/toolchain/hugegraph-spark-connector.md	No example for a PRIMARY_KEY vertex label or for ignored-fields	Added section 4.4 (software vertex, no id, ignored-fields=ISBN)	hugegraph-spark-connector/src/test/scala/org/apache/hugegraph/spark/connector/SinkExampleTest.scala:96
content/{en,cn}/docs/quickstart/toolchain/hugegraph-spark-connector.md	No example of an edge whose source and target use different id strategies	Added section 4.5 (created edge, customize source + primary key target)	hugegraph-spark-connector/src/test/scala/org/apache/hugegraph/spark/connector/SinkExampleTest.scala:157
content/{en,cn}/docs/quickstart/toolchain/hugegraph-spark-connector.md	Nothing said what SaveMode.Overwrite does	Added a note: overwrite returns a plain writer and does not delete existing data	hugegraph-spark-connector/src/main/scala/org/apache/hugegraph/spark/connector/writer/HGWriterBuilder.scala:35
content/{en,cn}/docs/quickstart/toolchain/hugegraph-spark-connector.md	Required options and key matching rules were not stated	Added an intro to section 5: keys lowercased and trimmed; data-type, label required; source-name, target-name required for edges; marked those rows "Required"	hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/options/HGOptions.java:73, hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/options/HGOptions.java:84, hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/options/HGOptions.java:89, hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/options/HGOptions.java:93, hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/options/HGOptions.java:97
content/{en,cn}/docs/quickstart/toolchain/hugegraph-spark-connector.md	host row did not mention that a scheme prefix is accepted	Noted that host may carry an http:// or https:// prefix	hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/client/HGClientHolder.java:47
content/{en,cn}/docs/quickstart/toolchain/hugegraph-spark-connector.md	username row omitted the fallback	Noted that the graph name is used when username is unset	hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/client/HGClientHolder.java:54
content/{en,cn}/docs/quickstart/toolchain/hugegraph-spark-connector.md	trust-store-file and trust-store-token rows omitted the https fallbacks	Documented ${connector.home.path}/conf/hugegraph.truststore (system property required) and the hugegraph default password	hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/client/HGClientHolder.java:65, hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/client/HGClientHolder.java:72, hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/constant/Constants.java:32, hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/constant/Constants.java:52
content/{en,cn}/docs/quickstart/toolchain/hugegraph-spark-connector.md	id row did not say AUTOMATIC is unsupported	Added that the AUTOMATIC id policy is not supported	hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/builder/VertexBuilder.java:79
content/{en,cn}/docs/quickstart/toolchain/hugegraph-spark-connector.md	batch-size row did not say the batch is per Spark task	Explained per-partition buffering and the flush at commit	hugegraph-spark-connector/src/main/scala/org/apache/hugegraph/spark/connector/writer/HGVertexWriter.scala:56, hugegraph-spark-connector/src/main/scala/org/apache/hugegraph/spark/connector/writer/HGEdgeWriter.scala:56
content/{en,cn}/docs/quickstart/toolchain/hugegraph-spark-connector.md	delimiter row claimed it also splits source-name and target-name; the code always splits those on ,	Limited delimiter to selected-fields and ignored-fields; noted , for source/target	hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/options/HGOptions.java:228, hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/options/HGOptions.java:240, hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/options/HGOptions.java:248, hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/options/HGOptions.java:260
content/{en,cn}/docs/quickstart/toolchain/hugegraph-spark-connector.md	No notes on runtime behaviour and limits	Added section 6 "Notes and Limitations": per-task HugeClient and LOADING mode, 128 byte vertex id limit, SET/LIST cardinality unsupported, date format yyyy-MM-dd HH:mm:ss in GMT+8, accepted boolean strings, empty vs null id handling; License moved to section 7	hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/client/HGLoadContext.java:66, hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/client/HGLoadContext.java:81, hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/builder/ElementBuilder.java:211, hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/utils/DataTypeUtils.java:54, hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/constant/Constants.java:48, hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/constant/Constants.java:50, hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/utils/DataTypeUtils.java:35, hugegraph-spark-connector/src/main/java/org/apache/hugegraph/spark/connector/utils/DataTypeUtils.java:39