Don't want to write this by hand? GodCraft sets minecraft:can_power_jump for you with a switch.Get GodCraftOverview
minecraft:can_power_jump is an entity component: it goes in the components object of a custom mob, or in one of its component groups. Lets a rider charge up a big jump by holding the jump button, like on a horse.
Example
Inside the components object of BP/entities/<name>.json (values are the defaults or placeholders):
BP/entities/<name>.json
{
"minecraft:can_power_jump": {}
}