Add documentation for joypad features (LEDs, adaptive triggers, motion controls, etc)

**Your Godot version:** 4.6

**Issue description:**
With Godot 4.6, thanks to the efforts of @Nintorch, special joypad features will be supported. These include:

- [x] https://github.com/godotengine/godot/pull/111681
- [ ] https://github.com/godotengine/godot/pull/111682
- [ ] https://github.com/godotengine/godot/pull/111714
- [ ] https://github.com/godotengine/godot/pull/111679
- [ ] https://github.com/godotengine/godot/pull/112680
- [ ] https://github.com/godotengine/godot/pull/116214
- [ ] https://github.com/godotengine/godot/pull/114642

These new methods will be documented in the class reference, but otherwise will remain somewhat hidden. I think we could add a page titled something like "Joypad-specific features" that describes these capabilities in greater detail, with code examples and diagrams as necessary.

This applies especially to the adaptive triggers feature; while I tried to describe them as well as I could in my PR suggestions for the class reference, I think diagrams [like I included here](https://github.com/godotengine/godot/pull/111682#issuecomment-3419253080) would go a long way for helping people understand how each mode works.

**URL to the documentation page (if already existing):** https://docs.godotengine.org/en/stable/tutorials/inputs/controllers_gamepads_joysticks.html (possibly?)