Improve database response time for listing user activity

What does this MR do?

This MR improves a database query to display activity of a given user to the currently logged in user. It leverages the user_interacted_tables table introduced in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/17327.

Are there points in the code the reviewer needs to double check?

1. Please double-check permissions are still respected properly.
2. Also, I ditched the LATERAL join because https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/17454#note_61882724 -- anything I'm not seeing?

Why was this MR needed?

For some users, displaying the user activity page times out. That is, the related query runs into the statement timeout.

A URL to test this is https://gitlab.com/ather-embitel (note we fail to show something for 'most recent activity' after a while).

Grafana links: Controller performance

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Review
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

Closes #40525 (closed)