"Happy Ghast" mob transportation

Allow players to tie mobs to the new Happy Ghast using leads for easy transportation across the Overworld. Ideally, mobs being transported via this method would not build up fall damage and perish the moment they make contact with the ground, the Happy Ghast is a lot slower and safer than the Elytra so it would make sense that they survive the ride.

Alternatively, allow mobs to sit on top of the Happy Ghast with the player and have them disembark the Ghast with us.