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.

[Tonisal-byte]

Just a general question, what are we going to be using the metadata for? Is it just to keep track of bugs? Will this be feeding into a pipeline of some sort?

[liunan-ms]

Metadata will be used for statistical purposes, like tracking the count of our intentional changes, upstreamable fixes (while we work on upstream, we can see the number of upstreamable goes down, which's another way to track our upstream contribution), category distribution of our changes (e.g. how many backport we carry, how many flaky tests we disabled, etc.) It will not be used in build or feed to pipelines.