feat(config): add optional metadata to component groups

[liunan-ms]

Summary

This PR is the second PR for adding metadata support, adding an optional [component-groups.<name>.metadata] block that reuses the existing OverlayMetadata schema — the required category plus optional commits, bugs, and upstreamable.

Metadata is documentation only: it does not affect how group members are resolved, filtered, or built. It gives component groups the same provenance-tracking surface that overlays already have, so consumers can record why a group exists (e.g. azl-pruning, backport-dist-git) and link back to commits / bugs.

Changes

• internal/projectconfig/component.go — reuse OverlayMetadata on ComponentGroup.
• internal/projectconfig/configfile.go — wire group-metadata validation into ConfigFile.Validate.
• internal/projectconfig/loader_test.go — coverage for the new field.
• docs/user/reference/config/component-groups.md — reference doc updates.
• schemas/azldev.schema.json + scenario snapshots — regenerated via mage docs.

Testing

• mage docs — schema and CLI docs regenerate cleanly (no diff after commit).
• Unit tests updated in loader_test.go.

Notes

• Metadata is excluded from component fingerprints, consistent with how overlay metadata is handled — editing it never invalidates build caches.
• No behavioral change to resolution or build.

[Copilot]

Pull request overview

Adds an optional [component-groups.<name>.metadata] block by reusing the existing OverlayMetadata schema, allowing component groups to carry documentation-only provenance (category/commits/bugs/upstreamable) and enforcing validation during config load.

Changes:

• Add Metadata *OverlayMetadata to ComponentGroupConfig and expose it in the JSON schema.
• Validate group metadata via ConfigFile.Validate() (reusing OverlayMetadata.Validate() rules).
• Add unit tests and update user docs / regenerated schema snapshots.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
internal/projectconfig/component.go	Adds optional metadata to component group config using OverlayMetadata.
internal/projectconfig/configfile.go	Hooks component-group metadata validation into ConfigFile.Validate().
internal/projectconfig/loader_test.go	Adds tests covering group metadata parsing/validation.
docs/user/reference/config/component-groups.md	Documents the new metadata block for component groups.
schemas/azldev.schema.json	Regenerated schema: adds component-groups.*.metadata referencing OverlayMetadata.
scenario/snapshots/TestSnapshotsContainer_config_generate-schema_stdout_1.snap	Regenerated snapshot reflecting schema update.
scenario/snapshots/TestSnapshots_config_generate-schema_stdout_1.snap	Regenerated snapshot reflecting schema update.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated no new comments.