Add support for merge request approval rules for migrated repository

Overview

Review possibilities of PRs in ADO and GitLab's MR. Add support for migration of policies that is possible to map "as is" (e.g. 4 eye principal, reset approvers in case of new commit etc).

Tasks

• Update docs if needed (workflow, runbooks, README, migration metrics, etc.)

Acceptance Criteria

• Existing UTs pass locally
• 100% code coverage on new code

@gitlab-org/professional-services-automation/tools/migration