Add Antarctica Map (#544)

## Description:
This PR adds the new Deglaciated Antarctica map(suggested by Backn). It
has 9 nations - most of the country territorial claims on the continent
and the "Penguin Empire".

fixes #545 

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

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

Nikola123

---------

Co-authored-by: Loymdayddaud <145969603+TheGiraffe3@users.noreply.github.com>

src/core/game/TerrainMapFileLoader.ts

@@ -42,6 +42,7 @@ const MAP_FILE_NAMES: Record<GameMapType, string> = {
   [GameMapType.BetweenTwoSeas]: "BetweenTwoSeas",
   [GameMapType.KnownWorld]: "KnownWorld",
   [GameMapType.FaroeIslands]: "FaroeIslands",
+  [GameMapType.DeglaciatedAntarctica]: "DeglaciatedAntarctica",
   [GameMapType.EuropeClassic]: "EuropeClassic",
 };