Extend GraphQL with policies overriding project approval settings in MR

What does this MR do and why?

This MR extends GraphQL with policies overriding project approval settings in MR so that we can show a warning icon near the approvals when the settings are being overridden.

FE is added in !175674 (merged).

References

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• FE changes: !175674 (merged)

MR acceptance checklist

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Screenshots or screen recordings

Generic / when policy details are not populated	With single policy	With multiple policies

How to set up and validate locally

1. Create a project
2. In the project, create a policy which overrides approval settings:

   approval_policy:
     - name: Any commit approvals
       description: ''
       enabled: false
       rules:
         - type: any_merge_request
           branch_type: protected
           commits: any
       actions:
         - type: require_approval
           approvals_required: 1
           role_approvers:
             - developer
         - type: send_bot_message
           enabled: true
       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: false
         require_password_to_approve: false
       fallback_behavior:
         fail: closed
   

3. Create MR and verify the data using GraphQL explorer:

   {
     project(fullPath: "<path-to-project>") {
       id
       mergeRequest(iid: "<mr-iid>") {
         id
         policiesOverridingApprovalSettings {
           name
           editPath
           settings
         }
       }
     }
   }

4. Update the violations to remove the link to Security::ApprovalPolicyRule

   MergeRequest.last.scan_result_policy_violations.update_all(approval_policy_rule_id: nil)

5. Verify that settings are still returned, with name and editPath being null

Related to #478175 (closed)