getJumpPower config +more #224

Describe the feature you have in mind.

1. a LivingEntity mixin that adjusts jump power to a configured number while wearing an active jetpack.
2. jetpacks should be disabled while touching a climbable block (vine, ladder, etc.) though this could be a config too.
3. when a distance above ground number is set, it should lower the acceleration incrementally, so the higher you go the less you can accelerate. if it's lowered by a set multiplier per block, the amount of blocks above the set height can be consistent across different configured accelerations. you could even set the block where acceleration reaches 0 as the configurable distance above ground value.
4. a config to disable the walking animation while flying.

Does this solve a particular problem?

1. the initial acceleration of the jump give the player too much velocity to start when i would prefer it to be gradual. this would allow players to disable the jump or weaken it.
2. climbing being prioritized feels more intuitive and user friendly.
3. just disabling thrust at a certain height doesn't feel very smooth and makes less sense in immersion.
4. to me it feels like creative mode flight and also doesn't make sense. feels like an overlooked detail but i could also see it being a stylized choice/personal preference