Minigun barrel rotation speed animation config

[GoldSloth]

Description of changes

Added animation modifier to change visual rotation speed of minigun barrels.

Intended usage in Content Packs/Users of the mod

Config in gun model java (minigunBarrelRotationSpeed).

Compatibility

Will not affect existing behaviour, including time until the minigun starts shooting.

Default speed =1 which is same rotation speed as present.

Other

This animation setting needs to be added to the GunType model setting overrides too.

Note I haven't actually tested this, it's just an example for xdeadstokex to review.