add a config to modify the speed of elytra

[huihiuhuai]

i dont know how modern servers handle elytras but it will be nice to have an config to modify the speed of elytra because elytra to so fast and fast movements cause lag

[Roadhog360]

This might be tricky. I'm not sure how feasible this is because the elytra is just based on physics. Slowing down physics could drastically cause the elytra's movement to be partially or completely bad. I would suggest that if your server can't handle loading chunks fast, to not use the elytra, or maybe disable fireworks boosting to limit how much ground the elytra can cover.