Allow transfer of ownership for threads

Community owners often hire community managers to write and post the threads used for pinned posts with instructions for using the channel. In the event that a community manager moves on to a new job, it would be nice to be able to transfer ownership of threads on a thread-by-thread basis to a new community manager -- or a new community owner in the event the original owner has decided to sell their community business.

This will help make clear that the message is still relevant and backed by the current community manager without the need to flood the Activity feed re-posting all the same content again. It would also allow the new community manager to make edits to the threads if needed.

To protect the community owner in the event a community manager leaves on bad terms, it would be best for this feature not to require active participation from the account the thread is being transferred away from. Instead, this would be something either the original thread owner could initiate for their own threads or someone with admin level access could initiate for threads belonging to any user.

To protect users from another user creating a thread with something embarrassing and then attributing it to them, the transfer should send the person taking over ownership an email and/or in-platform notification showing them the full content of the thread header and asking them to accept the transfer.

To protect community members from their original content being attributed to someone other than themselves without their knowledge, if an admin initiates the transfer, the system should send the thread's original owner an email saying which account the thread was transferred to and there should be edit history visible in the fine print under the thread's header post. Maybe something like "Author history" that only appears when an ownership transfer has been applied. Users can click this to see a record of everyone who's had ownership of the thread and in what order.

Personally, I can't think of a use case for transferring comments on threads or posts to text channels to another user. In the event the original owner of a thread added comments to it, too, I suggest those comments stay in place attributed to their original author.