Android: Document how to generate a .jks release keystore

**Your Godot version:**
3.x and 4.x

**Issue description:**
I don't have much experience with it myself but users often struggle to create a release keystore for Google Play. See https://github.com/godotengine/godot/issues/69337 where apparently Google Play hints that the user might need a .jks keystore, which is not the format we show how to generate.

**URL to the documentation page (if already existing):**
https://docs.godotengine.org/en/latest/tutorials/export/exporting_for_android.html#exporting-for-google-play-store