Option to disable alliances + 2 new modifiers for variety 😄 (#3392)

## Description:

Rex had this idea: "It would be funny to have an option in private
lobbies to disable alliances."
I added it as an option.
Now people can choose to live in constant fear of their neighbors 😆 

Also added two new public game modifiers for variety (only for the
special rotation):
- Alliances disabled (low probability)
- x2 gold multiplier (low probability)

Would be nice to squeeze this into v30, last minute?

## Please complete the following:

- [X] I have added screenshots for all UI updates
- [X] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [X] I have added relevant tests to the test directory
- [X] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:

FloPinguin

src/server/GameServer.ts

@@ -157,6 +157,9 @@ export class GameServer {
     if (gameConfig.startingGold !== undefined) {
       this.gameConfig.startingGold = gameConfig.startingGold;
     }
+    if (gameConfig.disableAlliances !== undefined) {
+      this.gameConfig.disableAlliances = gameConfig.disableAlliances;
+    }
   }
 
   private isKicked(clientID: ClientID): boolean {