Fix rgb underglow hsb not saving in settings.

[yiancar]

I have noticed that changing HSB for the rgb underglow subsystem would not save the new value in settings except if an effect change was involved.

This is because the save function is not called in the zmk_rgb_underglow_set_hsb function.
Interestingly it is called in all other set functions of the API.

Even more interestingly,

zmk/app/src/behaviors/behavior_rgb_underglow.c

Line 135 in 239baa4

on_keymap_binding_convert_central_state_dependent_params(struct zmk_behavior_binding *binding,

in the behavior binding file, even tho each keycode could correspont to one of the other functions of the API that directly maps to their intention; they all get remapped to the zmk_rgb_underglow_set_hsb.

In either case, zmk_rgb_underglow_set_hsb should call the save function.

PR check-list

• Branch has a clean commit history
• Additional tests are included, if changing behaviors/core code that is testable.
• Proper Copyright + License headers added to applicable files (Generally, we stick to "The ZMK Contributors" for copyrights to help avoid churn when files get edited)
• Pre-commit used to check formatting of files, commit messages, etc.
• Includes any necessary documentation changes.

[caksoylar]

Related: #1920