kcms/nightcolor: Add a graphic view of the day/night timings

Show the scheduled times and transitions for the day and night lighting in a graphical view that portraits a 0-24h horizontal axis, with icons for each state and a gradient with the actual temperature colors for the transitions.

This view is placed on top to avoid visual jittering (going up and down) between the different modes, and also clashing with other visual elements, like the manual location map. Logically it may belong better below the mode selector combobox, but when adding the geolocation privacy note it would get moved.

I would like for this to go on 6.0 depending on how much it (doesn't) violate the soft freeze. Don't mind to target 6.1 instead.

CC: @bharadwaj-raju @nclarius @teams/vdg @teams/usability

FEATURE: 414809
FIXED-IN: 6

Automatic Location	Manual Location	Custom Timings
NightColor Off	Always On	PREVIOUS (Textual Info)

I'm aware of the work at !2066 (in fact the temperature color calculation is blatantly copied from there), and I very much like it. I think both MRs can work very well together.

This MR deals with the informational part, trying to showcase the expected times at a view glance for every mode, and IMHO the controls developed on !2066 can be added on top of this, replacing/complementing the more cumbersome manual timing settings.