GitLab Migration - migrate Merge Request approval rules
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### Problem
In https://gitlab.com/gitlab-org/gitlab/-/issues/369868 we added MR approvers to relations migrated with GitLab Migration, however MR approval rules [are not migrated yet](https://gitlab.com/gitlab-org/gitlab/-/issues/369868#note_1154880495).
MR approvals can be set on 4 levels:
- instance level, [docs](https://docs.gitlab.com/ee/user/admin_area/merge_requests_approvals.html)
- group level, [docs](https://docs.gitlab.com/ee/user/group/manage.html#group-merge-request-approval-settings)
- project level, [API docs](https://docs.gitlab.com/ee/api/merge_request_approvals.html#project-level-mr-approvals)
- MR level, [API docs](https://docs.gitlab.com/ee/api/merge_request_approvals.html#merge-request-level-mr-approvals)
### Proposed solution
Migrate MR approvals on project and MR level.
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