Adding MOVEMENT_EXERTION_MODIFIER as enchantment

[DPavonis]

Summary

Infrastructure "Added MOVEMENT_EXERTION_MODIFIER as an enchantment"

Purpose of change

Apparently the ability to modify movement exertion has been something the folks working on exoskeletons have been desiring, figured I'd take a crack at it.

Describe the solution

Added MOVEMENT_EXERTION_MODIFIER as a valid mathifiable enchantment (I think).

Describe alternatives you've considered

Hoping someone more competent than I am would come along and do this.

Testing

Modified a piece of armor's enchantment with MOVEMENT_EXERTION_MODIFIER then performed addition and multiplication operations on it. Seems to work.

Additional context

I am the metaphorical golden retriever at the keyboard telling myself I have no idea what I'm doing.