revisions_count: implement pagination for metadata revisions

[gnzng]

This PR closes #1389 (@genematx).

The revisions endpoint used the current page size as the count, so meta.count was just len(data) and the next pagination link was never generated.

Add CatalogNodeAdapter.revisions_count() (a COUNT query) and use it as the length hint in construct_revisions_response.

Checklist

• Add a Changelog entry
• Add the ticket number which this PR closes to the comment section

[checkmarx-gh-ast-us-povs]

Checkmarx One – Scan Summary & Details – 36d08141-642d-4038-96f4-a13ed275de79

Great job! No new security vulnerabilities introduced in this pull request

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[danielballan]

Thanks @gnzng! Looks good. I'll let @genematx get a look before this goes in. (Might be next week.)