Add approvalProjectRules to graphql endpoint

What does this MR do and why?

#362706 (closed) -> #372362 (closed)

Adds approvalRules collection under project.branchRules to display information about the approval rule for a given branch

How to set up and validate locally

1. Find a project.full_path of a project that has at least one protected branch

      rule = ApprovalProjectRule.last
      project = rule.project
      # If you don't have any protected branches this will fail to link the approval rule to the
      # protected branch and therefore will not be returned in GraphiQL.
      # Go to GDK and in the project (`"gdk.test:3000/#{project.full_path}/-/settings/repository"`)
      # create a protected branch and then link it with the code below.
      rule.protected_branches << project.protected_branches.first if rule.protected_branches.empty?
      project.full_path

2. Or add an approval rule for a branch via UI: https://docs.gitlab.com/ee/user/project/merge_requests/approvals/rules.html#add-an-approval-rule
3. Test permissions by assigning yourself as a guest to the project

     # user = User.find_by(email: "YOUR_EMAIL") # Use this if you do not use the default admin user in GDK
     user = User.find_by(email: "admin@example.com")
     project.add_guest(user)

4. Visit http://gdk.test:3000/-/graphql-explorer
5. Execute the following query, replace the full path value (as guest you should not see any rules)

{
  project(fullPath: FULL_PATH) {
    __typename
    branchRules {
      nodes {
        approvalRules {
          nodes {
            id
            name
            type
            approvalsRequired
            eligibleApprovers {
              nodes {
                name
              }
            }
          }
        }
      }
    }
  }
}

1. Make yourself a maintainer

     project.add_maintainer(user)

2. Execute the following query, replace the full path value (as maintainer you should see all the rules)

{
  project(fullPath: FULL_PATH) {
    __typename
    branchRules {
      nodes {
        approvalRules {
          nodes {
            id
            name
            type
            approvalsRequired
            eligibleApprovers {
              nodes {
                name
              }
            }
          }
        }
      }
    }
  }
}

"All branches" and "All protected branches"

The approval rules created for "All branches" and "All protected branches" are going to be displayed separately: #372362 (comment 1090472612)

MR acceptance checklist

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