Add GraphQL API for policy violations

What does this MR do and why?

This MR exposes the policy violations in GraphQL API.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

How to set up and validate locally

1. Create a project
2. Create .gitlab-ci.yml:

   include:
     - template: Jobs/Secret-Detection.gitlab-ci.yml
   
   build-job:
     script:
       - echo "Compiling the code..."
       - echo "Compile complete."

3. Create a policy:

   type: approval_policy
   name: Sec & Lic
   description: ''
   enabled: true
   rules:
     - type: scan_finding
       scanners: []
       vulnerabilities_allowed: 0
       severity_levels: []
       vulnerability_states:
         - new_needs_triage
         - new_dismissed
         - detected
         - confirmed
         - dismissed
         - resolved
       branch_type: protected
     - type: license_finding
       match_on_inclusion_license: true
       license_types:
         - BSD 3-Clause "New" or "Revised" License
       license_states:
         - newly_detected
       branch_type: protected
     - type: any_merge_request
       branch_type: protected
       commits: unsigned
   actions:
     - type: require_approval
       approvals_required: 1
       role_approvers:
         - developer

4. Create MR with violation:

   diff --git a/.env b/.env
   new file mode 100644
   index 0000000000000000000000000000000000000000..ee4bf74ac3b632173dafc09e74ecd68c298bdfa1
   --- /dev/null
   +++ b/.env
   @@ -0,0 +1 @@
   +AWS_TOKEN=AKIAZYONPI3G4JNCCWGQ
   \ No newline at end of file

5. Merge the secret so that it becomes a previously-existing vulnerability. The vulnerability should show up in Secure -> Vulnerability report.
6. Create a new MR, adding a new leaked secret. Example:

   diff --git a/.env b/.env
   index ee4bf74ac3b632173dafc09e74ecd68c298bdfa1..d791cd2180779bf094bd017e07b12c1fad506c2c 100644
   --- a/.env
   +++ b/.env
   @@ -1 +1,2 @@
   -AWS_TOKEN=AKIAZYONPI3G4JNCCWGQ
   \ No newline at end of file
   +AWS_TOKEN=AKIAZYONPI3G4JNCCWGQ
   +AWS_TOKEN2=AKIAZYONPI3G4JNCCWGZ
   \ No newline at end of file

7. Query the data presented in the bot comment via GraphQL API (/-/graphql-explorer):

{
  project(fullPath: "<project-path>") {
    mergeRequest(iid: "<iid>") {
      id
      title
      policyViolations {
        policies {
          name
          reportType
        }
        newScanFinding {
          name
          reportType
          severity
          location
          path
        }
        previousScanFinding {
          name
          reportType
          severity
          location
          path
        }
        anyMergeRequest {
          name
          commits
        }
        licenseScanning {
          license
          dependencies
          url
        }
        errors {
          error
          message
          reportType
          data
        }
        comparisonPipelines {
          reportType
          source
          target
        }
      }
    }
  }
}

Related to #433406