Create new policy for Projects::BranchRules::MergeRequestApprovalSetting
<!--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=520015)
</details>
<!--IssueSummary end-->
We need a new policy to handle the merge request approval settings.
This should include settings for
- `create_merge_request_approval_settings`
- `read_merge_request_approval_settings`
- `update_merge_request_approval_settings`
- `delete_merge_request_approval_settings`
issue