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/core/Schemas.ts

@@ -217,6 +217,8 @@ export const GameConfigSchema = z.object({
       isCrowded: z.boolean(),
       isHardNations: z.boolean(),
       startingGold: z.number().int().min(0).optional(),
+      goldMultiplier: z.number().min(0.1).max(1000).optional(),
+      isAlliancesDisabled: z.boolean(),
     })
     .optional(),
   nations: z
@@ -230,6 +232,7 @@ export const GameConfigSchema = z.object({
   infiniteTroops: z.boolean(),
   instantBuild: z.boolean(),
   disableNavMesh: z.boolean().optional(),
+  disableAlliances: z.boolean().optional(),
   randomSpawn: z.boolean(),
   maxPlayers: z.number().optional(),
   maxTimerValue: z.number().int().min(1).max(120).optional(), // In minutes

src/core/configuration/Config.ts

@@ -74,6 +74,7 @@ export interface Config {
   donateTroops(): boolean;
   instantBuild(): boolean;
   disableNavMesh(): boolean;
+  disableAlliances(): boolean;
   isRandomSpawn(): boolean;
   numSpawnPhaseTurns(): number;
   userSettings(): UserSettings;

src/core/configuration/DefaultConfig.ts

@@ -240,6 +240,9 @@ export class DefaultConfig implements Config {
   disableNavMesh(): boolean {
     return this._gameConfig.disableNavMesh ?? false;
   }
+  disableAlliances(): boolean {
+    return this._gameConfig.disableAlliances ?? false;
+  }
   isRandomSpawn(): boolean {
     return this._gameConfig.randomSpawn;
   }

src/core/game/Game.ts

@@ -243,6 +243,8 @@ export interface PublicGameModifiers {
   isCrowded: boolean;
   isHardNations: boolean;
   startingGold?: number;
+  goldMultiplier?: number;
+  isAlliancesDisabled: boolean;
 }
 
 export interface UnitInfo {

src/core/game/PlayerImpl.ts

@@ -477,6 +477,9 @@ export class PlayerImpl implements Player {
   }
 
   canSendAllianceRequest(other: Player): boolean {
+    if (this.mg.config().disableAlliances()) {
+      return false;
+    }
     if (other === this) {
       return false;
     }