kcm: Add tooltip explaining PipeWire profiles to combobox

This adds a tooltip to the Profile combobox explaining what they're meant for. For such a prominent thing in the UI, I think they warrant some explanation, because they are not obvious.

See here for info: https://gitlab.freedesktop.org/pipewire/pipewire/-/wikis/FAQ#what-is-the-pro-audio-profile https://docs.pipewire.org/page_man_pipewire-devices_7.html#device-param__alsa_card_profiles

I'm still trying to understand what exactly these profiles are myself, and I'm not sure if this is the best place for this explanation text (it's pretty long for a tooltip), so I'd appreciate any help/guidance!