fix: not returning to mainmenu when reconnect fails

[LPLafontaineB]

Description (*)

This PR does three things: first it adds null checks to prevent null reference exceptions, then it adds a mechanism for the host to tell the clients when it voluntarily quits a game, so that if they quit using the in-game quit button, they will not attempt to reconnect and simply display a message instead. Finally, it reduces the number of reconnection attempts to 1 to avoid an issue that seems linked to Relay, until further investigation allows us to better understand that bug (see MTT-2794 for details)

Related Pull Requests

Issue Number(s) (*)

Fixes issue(s): MTT-2786 and MTT-2795

Manual testing scenarios

1. Start a game as a host
2. Join with a client
3. With the host, leave the session via the in-game quit button
4. See the client is disconnected and returned to the main menu and doesn't try to reconnect
5. Start another game with a host and client
6. End the play mode if in editor or quit the application if using a build (not via the in-game quit button)
7. See the client attempting to reconnect, then failing and going back to the main menu

Questions or comments

On hold because will have to wait until #523 is merged first, as this is depending on a fix introduced by this other PR.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds are green)

[SamuelBellomo]

there's a few things that shouldn't be workarounds though, no? Only the 1 reconnect attempt limit should be a workaround?

[LPLafontaineB]

there's a few things that shouldn't be workarounds though, no? Only the 1 reconnect attempt limit should be a workaround?

Auto-reconnect as a whole was flagged as a workaround though and will not be in develop until pre.7 which should have the fix needed to remove the workaround auto-reconnect used