UI: Add Color Temperature unit

The current temperature unit adjusts to Celsius or Fahrenheit based on
unit system, but specifically for color temperatures the convention is
to display them in Kelvin, and it'd be strange to e.g. see 11240°F when
opening the white balance panel.

Therefore, this adds a dedicated Color Temperature unit, and uses it
for the two existing blackbody temperature inputs in shader nodes.

Pull Request: https://projects.blender.org/blender/blender/pulls/123337

source/blender/python/intern/bpy_utils_units.cc

@@ -53,6 +53,7 @@ static const char *bpyunits_ucategories_items[] = {
     "POWER",
     "TEMPERATURE",
     "WAVELENGTH",
+    "COLOR_TEMPERATURE",
     nullptr,
 };