Mark comment as abuse or spam

Description

• For issue comment or merge request comment.
• Master role has permission to mark a comment as abuse or spam.
• Master role has permission to unmark a comment as abuse or spam.
• If a comment is marked, the content of the comment is replaced with a message indicating it is abuse or spam. The original commenter and timestamp of the comment is not changed and is still visible. The original content is not visible, but is not deleted from the system.
• If a comment is marked, nobody has permission to edit the comment.
• If a comment is unmarked, the original content is visible again, and there is nothing in the UI indicating that it was previously marked.

Out of scope

• No system notes.
• No reporting by regular users. Just limited to Master role.
• No timestamps of marking / unmarking. No audit trail.