Add Achiran (#2280)

## Description:

Describe the PR.
Adds the Halloween Special Map - Achiran. It has 4 nations and will be
playable in game for a period of around 2 weeks during the Halloween
event.

## 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:

DISCORD_USERNAME
Nikola123

resources/lang/en.json

@@ -193,7 +193,8 @@
     "japan": "Japan",
     "yenisei": "Yenisei",
     "pluto": "Pluto",
-    "montreal": "Montreal"
+    "montreal": "Montreal",
+    "achiran": "Achiran"
   },
   "map_categories": {
     "continental": "Continental",