Serialize inline serialized_dashboard to a JSON string early

[Sankalp-Mittal]

Summary

Marshal an inline (structured) serialized_dashboard to a JSON string in phases.Initialize, mirroring ConfigureGenieSpaceSerializedSpace, so the value is always a plain string by the time the deploy engine sees it.

Why: a map left in config versus a JSON round-trip in state decode integers differently (Go int vs float64), so the direct engine reported false serialized_dashboard drift on every plan. The remote also comes back serialized, so a deep diff of a map against a string can never converge. Normalizing to a string up front makes config-side and state-side carry the same value.

Changes

• configure_dashboards_serialized_dashboard.go — reject setting both file_path and serialized_dashboard; switch on the inline value kind (string/nil/invalid pass through, map/sequence → json.Marshal, other → error). Keeps the existing file_path read.
• New test configure_dashboards_serialized_dashboard_test.go — the first test for this mutator (7 cases, mirroring the genie mutator's test).
• dashboard.go prepareDashboardRequest — dropped the map-marshal branch; a nil/string/default type switch, mirroring prepareGenieSpaceRequest.
• convert_dashboard.go — removed the now-dead marshalSerializedDashboard (convert.Normalize maps the string straight onto the schema's string field) and its call.
• Test fixtures in convert_dashboard_test.go and all_test.go updated to the always-string reality.

Plan-output change

The direct-engine plan for the change-serialized-inline acceptance test now shows serialized_dashboard as a JSON string in new_state.value and changes.old/new, instead of a structured map — so they're comparable to the remote string and the false drift is gone. The terraform variant and the create-path test are unchanged (tfdyn already marshaled to a string).

Notes

• Stacked on sankalp-mittal/dashboards-serialized-inline (Add acceptance test for inline serialized_dashboard #6463).
• Does not touch the hashing code (that's the top PR, direct: store a dashboard contents digest in state instead of the contents #6105).
• Verified: fmt, lint-q (0 issues), go vet, full build, unit tests, and the dashboards/migrate/validate acceptance suites all pass.

This pull request and its description were written by Isaac.

[github-actions]

Approval status: pending

/acceptance/bundle/ - needs approval

Files: acceptance/bundle/resources/dashboards/change-serialized-inline/out.plan.direct.json
Suggested: @denik
Also eligible: @pietern, @janniklasrose, @shreyas-goenka, @andrewnester, @lennartkats-db, @anton-107

/bundle/ - needs approval

6 files changed
Suggested: @denik
Also eligible: @pietern, @janniklasrose, @shreyas-goenka, @andrewnester, @lennartkats-db, @anton-107

_{Any maintainer (@andrewnester, @anton-107, @denik, @pietern, @shreyas-goenka, @simonfaltum, @renaudhartert-db, @janniklasrose, @lennartkats-db, @rugpanov, @rclarey) can approve all areas.
See OWNERS for ownership rules.}