Merge branch '21109-discussion-resolve-runs-a-single-update-query-per-note-but-should-run-a-single-update-query-for-all-notes-instead' into 'master'

Optimize discussion notes resolving and unresolving

## What does this MR do?

Optimize discussion notes resolving and unresolving

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

Some changes had to be made to the discussion spec to account for the fact that notes are not  individually updated now. I only focused on adapting them for the purpose of the regression fix, but admittedly they could be further improved in readability.

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

Closes #21109

See merge request !6141