When updating password of a user, ask whether sessions should be logged out

[jcgruenhage]

I used to reset passwords for people by updating the hash in the database, but I had started using this admin panel a few times by now, and a user has just informed me that they were logged out of every session. While this is documented plainly in the admin API docs of Synapse, the main use of this dashboard is that it reduces the barrier and provides abstractions. In this case though, the abstraction is quite dangerous, as it can lead to accidental data loss. The API, starting with Synapse 1.61.0, does provide the option to no log out users. This option should be exposed if available, and if not, a warning to the admin using the panel should be displayed, that you'll be logging out all of this users devices, and that they might loose access to their whole message history.