Refactor naming of GraphQL files, queries and mutations to follow the recommended snake_case pattern
The following discussion from !34221 should be addressed:
- [ ] @sarahghp started a [discussion](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/34221#note_358579761): (+1 comment)
> Also, I know this hasn't changed, but if you wanted to, you could update these to snake_case while you're in here, GraphQL'ing.
issue