Implement a "ka-ching" sound effect on kill (#2097)

## Description:
Building off of [this
PR](https://github.com/openfrontio/OpenFrontIO/pull/2090) which
implemented music, I extend this functionality to add sound effects.
Diff will be reduced if and when that PR gets merged!

I think the game would benefit from more sound effects, and adding a
"ka-ching" sound effect on kill seems like an easy place to start.

The ka-ching sound effect was found
[here](https://freesound.org/people/AKkingStudio/sounds/684165/) and is
licensed under Creative Commons.

## 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

Demo video with sound:

https://github.com/user-attachments/assets/18c857a4-a741-492a-bbc1-68d4f3ba38da


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

---------

Co-authored-by: icslucas <carolinacarazolli@gmail.com>

src/core/game/UserSettings.ts

@@ -176,4 +176,12 @@ export class UserSettings {
   setBackgroundMusicVolume(volume: number): void {
     this.setFloat("settings.backgroundMusicVolume", volume);
   }
+
+  soundEffectsVolume(): number {
+    return this.getFloat("settings.soundEffectsVolume", 1);
+  }
+
+  setSoundEffectsVolume(volume: number): void {
+    this.setFloat("settings.soundEffectsVolume", volume);
+  }
 }