Update 8.14-rc1 migrations to minimize downtime and deploy time
## What does this MR do?
Modify 8.14-rc1 migrations and code to minimize downtime and deploy time
## Are there points in the code the reviewer needs to double check?
No
## Why was this MR needed?
8.14-rc1 migrations took too much time in staging, so we didn't want to take too much downtime in production
## Does this MR meet the acceptance criteria?
- Tests
- [x] Added for this feature/bug
- [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - 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#24386
See merge request !7427
6eeff67c6e