[DOCINT-2096] docs: enable Document Revisions guide navigation

[yoasyo25]

Jira Ticket:

🎫   DOCINT-1853

PR should not be merged until PDM API Phase 2 is ready to be released to customers.

Summary

• Un-hides the Working with Document Revisions guide in the Document Management sidebar and on-site search (DOCINT-2096).
• Adds reverse Related Documentation links from Overview, Technical Guide, and Metadata Details.
• Replaces the private+beta warning with a beta-only callout, and documents the recycled download path (.../recycled_revisions/{id}/download).

Hold merge until document-service#7147 (DOCINT-1853) lands, so the REST reference and this guide agree on public vs private. Show Document Revision Permissions stays undocumented; the 7147 public/beta flip of that route is a mistake and will be reverted there.

Test plan

• ASDF_RUBY_VERSION=3.3.11 bundle exec jekyll build succeeds
• _site/search.json contains "title": "Document Revisions"
• Sidebar on _site/document-management-document-revisions.html includes Document Revisions
• Overview, Technical Guide, and Metadata Details Related Documentation blocks link to the guide
• Page no longer describes List Document Revisions as private
• Downloading a Revision documents both the active and recycled download paths
• Re-check after document-service#7147 merges that list + download routes are public+beta and permissions remains unpublished

---