Humans are severely skill issued ⚠️ Change HvN difficulty to Medium (#2971)

## Description:

For v29

HvN winrate is between 10 and 15%, but should be around 50%.

1. Change HvN difficulty to Medium
2. Little balance change in `NationAllianceBehavior`

## 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

src/server/MapPlaylist.ts

@@ -129,7 +129,7 @@ export class MapPlaylist {
       publicGameModifiers: { isCompact, isRandomSpawn, startingGold },
       startingGold,
       difficulty:
-        playerTeams === HumansVsNations ? Difficulty.Hard : Difficulty.Easy,
+        playerTeams === HumansVsNations ? Difficulty.Medium : Difficulty.Easy,
       infiniteGold: false,
       infiniteTroops: false,
       maxTimerValue: undefined,