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 {

src/server/MapPlaylist.ts

@@ -103,7 +103,9 @@ type ModifierKey =
   | "isCrowded"
   | "isHardNations"
   | "startingGold"
-  | "startingGoldHigh";
+  | "startingGoldHigh"
+  | "goldMultiplier"
+  | "isAlliancesDisabled";
 
 // Each entry represents one "ticket" in the pool. More tickets = higher chance of selection.
 const SPECIAL_MODIFIER_POOL: ModifierKey[] = [
@@ -113,6 +115,8 @@ const SPECIAL_MODIFIER_POOL: ModifierKey[] = [
   ...Array<ModifierKey>(1).fill("isHardNations"),
   ...Array<ModifierKey>(8).fill("startingGold"),
   ...Array<ModifierKey>(1).fill("startingGoldHigh"),
+  ...Array<ModifierKey>(1).fill("goldMultiplier"),
+  ...Array<ModifierKey>(1).fill("isAlliancesDisabled"),
 ];
 
 // Modifiers that cannot be active at the same time.
@@ -197,6 +201,7 @@ export class MapPlaylist {
         isCrowded,
         isHardNations,
         startingGold,
+        isAlliancesDisabled: false,
       },
       startingGold,
       difficulty: isHardNations ? Difficulty.Hard : Difficulty.Medium,
@@ -263,7 +268,14 @@ export class MapPlaylist {
       undefined,
       poolCountReduction,
     );
-    let { isCrowded, startingGold, isCompact, isRandomSpawn } = poolResult;
+    let {
+      isCrowded,
+      startingGold,
+      isCompact,
+      isRandomSpawn,
+      goldMultiplier,
+      isAlliancesDisabled,
+    } = poolResult;
     let isHardNations =
       hardNationsFromIndependentRoll ?? poolResult.isHardNations;
 
@@ -280,7 +292,9 @@ export class MapPlaylist {
           !isRandomSpawn &&
           !isCompact &&
           !isHardNations &&
-          startingGold === undefined
+          startingGold === undefined &&
+          goldMultiplier === undefined &&
+          !isAlliancesDisabled
         ) {
           excludedModifiers.push("isCrowded");
           const fallback = this.getRandomSpecialGameModifiers(
@@ -288,7 +302,13 @@ export class MapPlaylist {
             1,
             poolCountReduction,
           );
-          ({ isRandomSpawn, isCompact, startingGold } = fallback);
+          ({
+            isRandomSpawn,
+            isCompact,
+            startingGold,
+            goldMultiplier,
+            isAlliancesDisabled,
+          } = fallback);
           isHardNations =
             hardNationsFromIndependentRoll ?? fallback.isHardNations;
         }
@@ -321,8 +341,12 @@ export class MapPlaylist {
         isCrowded,
         isHardNations,
         startingGold,
+        goldMultiplier,
+        isAlliancesDisabled,
       },
       startingGold,
+      goldMultiplier,
+      disableAlliances: isAlliancesDisabled,
       difficulty: isHardNations ? Difficulty.Hard : Difficulty.Medium,
       infiniteGold: false,
       infiniteTroops: false,
@@ -482,6 +506,7 @@ export class MapPlaylist {
         playerTeams === HumansVsNations
           ? Math.random() < HARD_NATIONS_HVN_PROBABILITY
           : Math.random() < 0.025, // 2.5% chance
+      isAlliancesDisabled: false,
     };
   }
 
@@ -530,6 +555,8 @@ export class MapPlaylist {
         : selected.has("startingGold")
           ? 5_000_000
           : undefined,
+      goldMultiplier: selected.has("goldMultiplier") ? 2 : undefined,
+      isAlliancesDisabled: selected.has("isAlliancesDisabled"),
     };
   }