Make it possible to specify state config path via commandline or env variable

[strk]

At the moment an hard-coded path is used to automatically save SonoBus standalone state whenever anything changes (you join or leave a room, you change levels of users). Running multiple SonoBus applications (I've done this in bridging setup) make this problematic because the SAME state file is being contended by DIFFERENT applications.

The problem would be resolved by allowing the specification of a state file.