Resolve "Introduce merge check for policy violations"

What does this MR do and why?

If there is a policy violation, we need to block the MR until this violation has been resolved.

To test

1. Turn on feature flag policy_mergability_check and ensure you have a Docker runner

2. In the project, ensure that main is a protected branch.

3. Create .gitlab-ci.yml:

   include:
     - template: Jobs/Secret-Detection.gitlab-ci.yml
   
   test-job:
     stage: test
     script:
       - echo "Testing"

4. Go to Secure -> Policies -> New policy. Select "Merge request approval policy".

5. Switch to the .yaml mode and use the following YAML:

   type: approval_policy
   name: Security
   description: ''
   enabled: true
   rules:
     - type: scan_finding
       scanners: []
       vulnerabilities_allowed: 0
       severity_levels: []
       vulnerability_states: []
       branch_type: protected
   actions:
     - type: require_approval
       approvals_required: 1
       role_approvers:
         - developer
   approval_settings:
     block_branch_modification: true
     prevent_pushing_and_force_pushing: true
     prevent_approval_by_author: true
     prevent_approval_by_commit_author: true
     remove_approvals_with_new_commit: true
     require_password_to_approve: false
   fallback_behavior:
     fail: closed
   

6. Configure with a merge request && merge

7. Go back to the project and open a new MR

8. The MR should be blocked with security evaluation check and the security rule is optional

9. Create a .env file with `AWS_TOKEN=AKIAZYONPI3G4JNCCWGQ'

10. Push, and wait for the CI to run, and the mergeability check should fail

11. Fix the violation by removing the token and push

12. The MR should not fail the violation check

Related to #478861 (closed)