Add `forceclose` command

[eartharoid]

The close command (and button, if enabled) will prompt the ticket creator to close the ticket by clicking the confirmation button (which would open the feedback modal if enabled). The message should be different if the creator uses the command themselves instead of the staff. If there is no response after a while (configurable? 36 hours default?), close the ticket automatically. If staff use the command and the user is not in the guild anymore, close the ticket immediately.

An additional force-close command that only staff can use will not wait for the creator to respond.

Related idea.