feat(drive): add labels for structured file metadata (Labels API v2)

[dl-alexandre]

Summary

Add Google Drive Labels API v2 support for structured file metadata and enterprise content classification.

Current State

gog drive has no label/metadata taxonomy support. This is the Drive Labels API (not Gmail labels, which gog gmail labels already handles).

Proposed Commands

gog drive labels list                             # List available label schemas
gog drive labels get <labelId>                    # Get label schema details
gog drive labels file list <fileId>               # Labels applied to a file
gog drive labels file apply <fileId> <labelId> --fields '{"key":"value"}'
gog drive labels file remove <fileId> <labelId>

Use Cases

• Enterprise content classification (document types, retention policies)
• Project tagging with structured metadata
• Workflow automation based on label values
• Compliance and records management

API Notes

• API: https://developers.google.com/drive/labels/overview
• Additional scope: https://www.googleapis.com/auth/drive.labels
• Labels are structured metadata schemas defined at the organization level

Related

None — this is Drive Labels (structured metadata), distinct from Gmail labels.

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I've implemented this in another Drive CLI and can share implementation details if helpful.

[salmonumbrella]

Feel free to open a PR!