WIP: Remove per-entity tables

[JAORMX]

Summary

Fixes #4315

Change Type

Mark the type of change your PR introduces:

• [ ] Bug fix (resolves an issue without affecting existing features)
• [x] Feature (adds new functionality without breaking changes)
• [ ] Breaking change (may impact existing functionalities or require documentation updates)
• [ ] Documentation (updates or additions to documentation)
• [x] Refactoring or test improvements (no bug fixes or new functionality)

Testing

Outline how the changes were tested, including steps to reproduce and any relevant configurations. Attach screenshots if helpful.

Review Checklist:

• [x] Reviewed my own code for quality and clarity.
• [ ] Added comments to complex or tricky code sections.
• [ ] Updated any affected documentation.
• [ ] Included tests that validate the fix or feature.
• [ ] Checked that related changes are merged.

[jhrozek]

About the failures in artifact.go - I wonder if the path of least resistance (even with a bit of manual coding that might be thrown away later) would be to substitute the database lookups like GetArtifact with wrappers around GetEntity that would for now fulfill the same contract, in case of GetArtifact still return a pb.Artifact.

[github-actions[bot]]

This PR needs additional information before we can continue. It is now marked as stale because it has been open for 30 days with no activity. Please provide the necessary details to continue or it will be closed in 30 days.