[FEATURE] Zombie horses spawn naturally

[LeStegii]

Explanation

If this option is enabled, zombie horses will spawn with a certain chance instead of skeleton horses when a skeleton trap occours.

Why?

Currently, there is no option to get these mobs in survival minecraft. Adding them to this event makes them an uncommon mob, but still obtainable.

Additional information

This has been implemented in a similar way by PurpurMC.

https://github.com/PurpurMC/Purpur/blob/ver/1.19.3/patches/server/0027-Zombie-horse-naturally-spawn.patch