Refactor Rails initializers
<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=25845) </details> <!--IssueSummary end--> We currently have 100+ initializers in `config/initializers`. These are loaded by Rails alphabetically so ordering is important. We have a few of them that are numbered to force the order but they are inconsistent and there are duplicate numbers. `01_..`, `1_..`, etc.. This has caused a bug here: https://gitlab.com/gitlab-org/gitlab-ce/issues/55513 We should name these consistently and perhaps make it easier to insert initializers in between without having to rename a bunch of files. We should also consider reducing the number of files here.
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