docs: document v3 migration and v6 beta changes

[rustatian]

Document the v5-to-v6 plugin migration for the upcoming v3 release on release/v3.

Included Changes

• Add a migration guide for HTTP middleware order, H2C, logging and rotation, removed RPC codecs/exporters, and TCP default-build removal.
• Document named Jobs pools, AMQP v2 configuration, the new NSQ driver, and broker/storage fixes.
• Update gRPC reflection, Temporal worker capabilities, health checks, metrics, and tracing guidance.
• Cover pool and Goridge changes, the api/api-go/api-plugins split, slog interfaces, and context-aware plugin contracts. Clarify the unchanged Endure and tcplisten requirements.
• Replace obsolete Velox examples with a pinned v3 development build. Separate untagged PROXY protocol, static caching, pool, and Temporal changes from the selected beta versions.
• Document current beta limits, including BoltDB named-pool routing, memory expiration, allocation retry, and service restart behavior.
• Include zstd middleware documentation for feat: add zstd HTTP middleware zstd#1.
• Correct startup instructions, CORS and upload restrictions, queue and lock guarantees, and PHP/Go API examples.
• Repair the historical Lambda adapter mapping, execution limits, and bootstrap build.

Closed PRs

• feature: v2 config amqp, grpc interceptors #72: AMQP v2 pipeline configuration and unary gRPC interceptors.
• docs(http): document static middleware cache options #79: Static middleware prefixes, cache TTLs, cache limits, and ETag behavior.

[Copilot]

🟡 Changes recommended

There are a couple of documentation consistency/clarity issues (HTTP zstd page title format and static cache behavior description) that should be corrected to avoid confusing readers.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR consolidates and expands RoadRunner v3-related documentation by adding new docs pages/features (HTTP zstd middleware and gRPC interceptors) and updating existing pages to reflect newer configuration formats and behaviors.

Changes:

• Added new documentation pages for HTTP zstd middleware and gRPC unary interceptors, and linked them from navigation and existing guides.
• Reworked AMQP jobs pipeline documentation to describe versioned pipeline config formats (v2 nested exchange/queue vs legacy flat) and added operational notes (read-only RabbitMQ, RPC declaration behavior).
• Updated HTTP docs to include zstd in the HTTP middleware reference and refreshed static middleware caching/ETag documentation.

File summaries

File	Description
SUMMARY.md	Adds nav entries for HTTP zstd and gRPC Interceptors.
queues/amqp.md	Updates AMQP pipeline config docs (v2 nested format, legacy keys, permissions/RPC notes, migration/next links).
http/zstd.md	New page documenting HTTP zstd middleware availability, config, and behavior.
http/static.md	Updates static middleware docs with cache/prefix options and corrected ETag behavior description.
http/http.md	Adds zstd to the allowed HTTP middleware list and notes build requirement.
grpc/interceptors.md	New page documenting interceptor contract, config, ordering, and build examples.
grpc/grpc.md	Adds a cross-link to the new interceptors documentation.

Review details

• Files reviewed: 7/7 changed files
• Comments generated: 2
• Review effort level: Lite

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