Use Apollo/GraphQL to load branch list in `project_branch_selector.vue`
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### Description
The following discussion from !127893 should be addressed:
- [ ] @mrincon started a [discussion](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/127893#note_1493963617): (+3 comments)
> **Thought:** Apollo/GraphQL would be great at handling some of these optimizations under the hood. I am looking forward to a version of this that's migrates this component.
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