Wildcard V2: Add label hover style to `BaseControlInput`
Created by: courier-new
Adds the missing hover style that darkens the text to $gray-12
to the label for BaseControlInput
as featured in the Wildcard design files, which controls radio buttons and checkboxes:
https://user-images.githubusercontent.com/8942601/153955776-0de79914-2a92-4522-9cd5-ec41a8b35a80.mov
It's subtle but it's something.
"Valid" coloration (green for valid, red for invalid) overwrites this hover style.
Test plan
Verified visually in Storybook for both the checkbox and radio button components.