Keep threads alive for a specified amount of time

[ffamilyfriendly]

Allow selecting a certain time to keep a thread alive, instead of indefinitely. This is a pretty frequent request.
Users want threads to be alive longer than the discord max of 1W but not quite forever.

Not sure how we would implement this in a nice way. This could be an option on /watch, /batch, and /monitor where a custom duration could be selected with the default being forever. We would have to add a last activity field to the thread in our database to keep track of how long the thread has been inactive, along with a watch duration field as well to keep track on how long the user wants the thread to be watched for

[ffamilyfriendly]

We should also allow the user to specify what happens to the thread when the timer elapses such as deleting the thread, unwatching it, locking it, and so forth