adding invalid state transition test + unit test

[dgkanatsios]

This PR introduces a check for invalid state transitions between two subsequent heartbeat requests as well as a corresponding unit test. A couple of points

• the check for invalid state transition currently only checks for transition from StandingBy to Initializing. We expect to expand with more checks in the future
• we want to kill LocalMultiplayerAgent when an invalid transition happens. This is to facilitate running LMA in a CI/CD environment
• the way that we kill the LMA process is by using the IHostApplicationLifeTime object. We've used this way in a Thundernetes sample and has worked great so far. Not sure if there is a better way.