Memoize MR merged/closed events retrieval

What does this MR do?

Memoize a database call that is execute 3 consecutive times

Why was this MR needed?

To speed up MR pages

What are the relevant issue numbers?

#14202 (moved) , #19490 (closed)

Screenshots (if relevant)

The query is fast most of the times, but we can avoid the 3 call counts to the database

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• [ ] Documentation created/updated
• [ ] API support added
• Tests
  • [ ] Added for this feature/bug
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together