[PR #8086/66ea16ce backport][3.105] Speed up RepositoryVersion saves on add/remove content

[patchback]

This is a backport of PR #8086 as merged into main (66ea16c).

Was asking sol to take a look at our RepoContent/content_ids problem and it pointed this out. Postgres can't optimize the update to be on the HOT path since the indexes become targets without specifying the fields, or so the AI says. Can't hurt

Assisted-by: gpt-5.6-sol

📜 Checklist

• Commits are cleanly separated with meaningful messages (simple features and bug fixes should be squashed to one commit)
• A changelog entry or entries has been added for any significant changes
• Follows the Pulp policy on AI Usage
• (For new features) - User documentation and test coverage has been added

See: Pull Request Walkthrough