Extend GraphQL approval rules with indication of invalid rules

What does this MR do and why?

This MR extends ApprovalRuleType GraphQL type, adding two fields:

• invalid
• allow_merge_when_invalid

It changes the behavior of security policy approvals only. In case the rules become invalid, the approvals will fail closed, instead of failing open.

Screenshots or screen recordings

The MR affects the following:

How to set up and validate locally

1. Create a new security policy with secret detection and require approval from one user
2. Configure with merge request & Merge
3. Open an MR which adds a leaked secret, thus violating the policy
4. Block the user used in the security policy
5. Use GraphiQL to query the new fields. invalid should be true, approved should be true and allowMergeWhenInvalid should be true for the secret detection rule.

   {
     project(fullPath: "<project-path>") {
       id
       mergeRequest(iid: "<MR-iid>") {
         id
         approvalState {
           invalidApproversRules {
             id
           }
           rules {
             id
             type
             approved
             approvalsRequired
             name
             section
             invalid
             allowMergeWhenInvalid
           }
         }
       }
     }
   }

6. Enable the new feature flag:

   Feature.enable(:invalid_scan_result_policy_prevents_merge)

7. invalid should be true, approved should be false and allowMergeWhenInvalid should be false for the secret detection rule

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 #389905 (closed)