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

resources/lang/en.json

@@ -193,6 +193,7 @@
     "infinite_gold": "Infinite gold",
     "infinite_troops": "Infinite troops",
     "compact_map": "Compact Map",
+    "disable_alliances": "Disable alliances",
     "max_timer": "Game length (minutes)",
     "max_timer_placeholder": "Mins",
     "max_timer_invalid": "Please enter a valid max timer value (1-120 minutes)",
@@ -414,6 +415,7 @@
     "infinite_troops": "Infinite troops",
     "donate_troops": "Donate troops",
     "compact_map": "Compact Map",
+    "disable_alliances": "Disable alliances",
     "enables_title": "Enable Settings",
     "player": "Player",
     "players": "Players",
@@ -431,9 +433,12 @@
     "teams_Trios": "Trios (teams of 3)",
     "teams_Quads": "Quads (teams of 4)",
     "teams_Humans Vs Nations": "Humans vs Nations",
-    "starting_gold": "Starting gold",
     "crowded": "Crowded modifier",
     "hard_nations": "Hard Nations",
+    "gold_multiplier": "Gold multiplier",
+    "gold_multiplier_placeholder": "2.0x",
+    "starting_gold": "Starting Gold (Millions)",
+    "starting_gold_placeholder": "5",
     "leave_confirmation": "Are you sure you want to leave the lobby?"
   },
   "team_colors": {
@@ -478,7 +483,9 @@
     "compact_map": "Compact Map",
     "crowded": "Crowded",
     "hard_nations": "Hard Nations",
-    "starting_gold": "{amount}M Starting Gold"
+    "starting_gold": "{amount}M Starting Gold",
+    "gold_multiplier": "x{amount} Gold Multiplier",
+    "disable_alliances": "Alliances Disabled"
   },
   "select_lang": {
     "title": "Select Language"