Add an Antarctica map 🐧 (#3740)

## Description:

(re-submission of older PR because the old one had too many merge
conflicts)

Re-adds and reworks the previously April Fools "Reglaciated Antarctica"
as a new map, this time with proper elevation data: Map of Antarctica
centered in the South Pole.

The "appeal" of this a map is that it has no green terrain. (As such it
has a really low rotation number (of 1). )

This also completes the Continental map category (antarctica was the
only continent out of the traditional 7 missing).


https://github.com/user-attachments/assets/28302464-c533-483e-8a1b-2699093921ff

The base map image is a composite of 2 relief maps from 2 different
sources, both properly credited

## 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:

tri.star1011

Co-authored-by: iamlewis <lewismmmm@gmail.com>

src/server/MapPlaylist.ts

@@ -91,6 +91,7 @@ const frequency: Partial<Record<GameMapName, number>> = {
   Conakry: 3,
   Caucasus: 5,
   BeringSea: 5,
+  Antarctica: 1,
 };
 
 const TEAM_WEIGHTS: { config: TeamCountConfig; weight: number }[] = [