WLED - Expose effect speed and intensity as input_number sliders

Add two number_input sliders, one for effect brightness and one for effect intensity. This allows the user to control effect speed and intensity directly from home assistant, without having to interact with the WLED web interface.

This will also allow for convenient getting/setting of these values in HA automations or in NodeRED with the HA nodes.

Going through WLED feature requests and noticed this one. This one has already been implemented.