Adds admin verb to reestablish connection to the database

Used mainly when the database goes down, is brought back up, but you don't want to wait for the next round for the failed connections counter goes below 5.

Any holder holding admin can use it (like reload), (per consultation with tgstation admins and sos on what they thought made the most sense) but only +DEBUG admins can make it attempt to reconnect when the database appears connected (per request of sos).