Add branchRules to project in graphql endpoint

What does this MR do and why?

This MR add a paginated branchRules node to the projects query. The returned values are actually protected branches. In a future MR we will add additional nodes nested within the branchRules node containing information about the different types of branch rules. This information will be presented in a single location as part of an ongoing effort to improve the UX.

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

I have added a new ability to the protected branches policy which currently follows the same rules as the create/update/destroy abilities.

How to set up and validate locally

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

      project = ProtectedBranch.last.project
      project.full_path

2. 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)

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

    {
      project(fullPath: "FULL_PATH") {
        branchRules {
          nodes {
            name
          }
        }
      }
    }

5. Make yourself a maintainer

     project.add_maintainer(user)

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

    {
      project(fullPath: "FULL_PATH") {
        branchRules {
          nodes {
            name
          }
        }
      }
    }

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.