[Hotfix] Halt tick processing if the server isn't able to reach the internet

What has been done in this MR?

• If the watchdog is enabled (server.watchdog_enabled), it will now also monitor for an active internet connection
• Internet connection is detected by trying to connect to a configurable URL (server.connectivity_check_url) (defaults to http://google.com)
• Configurable timeout for connection attempt (server.connectivity_timeout) (defaults to 500 milliseconds)
• If a loss of connection is detected, all tick processing is paused until connectivity resumes. The disconnection queue is still processed and world tick count is still incremented, but there is otherwise 0 game logic processing.

What should testers check?

• Testers can't really check without otherwise seriously disrupting the test server. Be at ease, I have very thoroughly tested this myself.

• I have tested these changes thoroughly.

• I used the relevant Zaros tool for any JSON edits where possible, and have attached screenshots of any changes.