WIP: Use a new table for user contribution stats

What does this MR do?

It defers the user contribution stats to a new table, instead of the events table.

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

Why was this MR needed?

This will allow down sizing the events table.

Screenshots (if relevant)

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 merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

#22623 (moved)

@yorickpeterse Hi, what do you think of the migration?

@leibo I posted some comments on the migration above.

Added 1 commit:

• 0cd5c1c1 - Use a new table for user conribution stats

Compare with previous version

@yorickpeterse Hi, I fixed according to your comments, WDYT?

Reassigned to @leibo

Added 1 commit:

• 76160d06 - Use a new table for user conribution stats

Compare with previous version

Resolved all discussions

@yorickpeterse fixed, moving on I think

@leibo Looks good so far

Mentioned in issue #24344 (closed)

Added ~164274 label

Added 1 commit:

• 31c2b3b1 - Use a new table for user conribution stats

Compare with previous version

@yorickpeterse Added the model and Sidekiq worker, take a look.