Describe the enhancement
My proposal is to add an optional config feature that makes it so the up and down controls are inverted when flying with elytra - this applies for when you move the mouse up, the player goes down instead of up and vice versa.

As someone who is currently in the process of learning to fly a glider, I find this much more realistic and convenient to use.

This is already an option, check out the "invert pitch" toggle in the config.