Readd Yenisei (#3145)

## Description:
This PR readds the Yenisei map, with it being about 3 times smaller than
before. I haven't updated the en.json file, as it still has the string
for the map, which was probably forgotten when the map got removed from
the repo.
## 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

src/server/MapPlaylist.ts

@@ -66,6 +66,7 @@ const frequency: Partial<Record<GameMapName, number>> = {
   AmazonRiver: 3,
   Sierpinski: 10,
   TheBox: 3,
+  Yenisei: 6,
 };
 
 interface MapWithMode {