Expose :admin_work_item permission on GraphQL

What does this MR do and why?

Exposes :admin_work_item permission for WorkItemType on GraphQL.

How to set up and validate locally

1. Create any work item using the UI. Can be a regular issue.
2. Get its global id on GraphQL or on console using WorkItem.last.to_global_id.to_s
3. Execute the following GraphQL query:

query workItem {
  workItem(id: "gid://gitlab/WorkItem/613") {
    title
    userPermissions {
      adminWorkItem
    }
  }
}

If user is reporter+ the field should return true otherwise false.

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.