Real time notification when Playnite is running

[andrew-codes]

In order to aid in automation of starting, stopping and restarting games, it would be nice to be notified when Playnite starts and stops running. This will allow automation to know whether Playnite is running or not on the gaming host machine.

• [ ] MQTT message is broadcast when Playnite first connects to the MQTT broker
• [ ] MQTT message is broadcast when Playnite disconnects from the MQTT broker
• [ ] Switch entity can be automatically created in Home Assistant from the messages
  • [ ] MQTT messages support Home Assistant device discovery format
• [ ] Graph API provides a subscription to Playnite's status

[cvele]

There is already a "connected" topic, but the message is not persistent. This could potentially be resolved by simply making that message persistent. However, I’m concerned about how the plugin will behave when MQTT goes offline (due to restarts, network issues, etc.), though that's a separate issue. I've already submitted a brief PR to try and address this.