Resolve "Introduce merge check for merge request approval policy evaluation"

What does this MR do and why?

After !158203 (merged) is merged, we now track the state of the scan status. We can use this state to determine if the scan results are evaluated or not.

We create a new mergeability check to enforce that the scan results are evaluated before merging.

How to set up and validate locally

1. Create a project

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. There should be a secret_detection job running and an approval rule "Security" enforced by the policy.

Related to #444459 (closed)