Sync any_merge_request rules regardless of pipelines

What does this MR do and why?

This MR makes change to the logic which removes required approvals for any_merge_request rules.

Currently, the required approvals are removed for policy-compliant MRs only if there is a CI configuration and security scans are included in the pipeline (e.g. template: Jobs/Secret-Detection.gitlab-ci.yml).

Because any_merge_request rule approvals only depend on whether the commits are unsigned or signed, this change will make it so that the approvals are removed immediately after a change in MR regardless of the pipeline setup.

The changes in this MR are done behind a feature flag scan_result_any_merge_request that is disabled by default.

Screenshots or screen recordings

Before	After
CleanShot_2023-10-12_at_12.15.50	CleanShot_2023-10-12_at_12.26.22

How to set up and validate locally

1. In rails console enable the feature flag

   Feature.enable(:scan_result_any_merge_request)

2. Create a policy targeting unsigned commits. Go to Policies -> New scan result policy -> .yaml mode. Example YAML:

   type: scan_result_policy
   name: Unsigned
   description: ''
   enabled: true
   rules:
     - type: any_merge_request
       branch_type: protected
       commits: unsigned
   actions:
     - type: require_approval
       approvals_required: 1
       user_approvers_ids:
         - 4
         - 1
   approval_settings:
     block_protected_branch_modification: true
     prevent_approval_by_author: true
     prevent_approval_by_commit_author: true
     remove_approvals_with_new_commit: true
     require_password_to_approve: true

3. Set up signed commits
4. Create MR with a signed commit
5. Verify the approvals for the policy rule are not required
6. Add an unsigned commit (for example via WebIDE)
7. Verify the approvals are required
8. Force push so that only the signed commits are in the MR again
9. Verify the approvals are optional again

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #418752 (closed)