Add edited by information to GraphQL WorkItem type

What does this MR do and why?

Adds the following fields to the root of WorkItemType

• edited -> if the work item has been edited
• last_edited_by -> last user that edited the work item
• last_edited_at -> timestamp of last edit

These fields are updated whenever a user updates the title or description of a work item

How to set up and validate locally

1. Change the title or description of a work item or issue via web interface or API. Note the global ID of the updated issue/work item
2. Fetch the same work_item / issue via the GraphQL API using a query like:

{
  workItem(id: "gid://gitlab/WorkItem/93810566") {
    id
    widgets {
      type
      ... on WorkItemWidgetDescription {
        lastEditedAt
        lastEditedBy {
          webPath
        }
      }
    }
  }
}

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 #365998 (closed)