[APP-1310] Button cleanup (#8754)
* Rm gradient buttons from Storybook
* TEMP move storybook button section
* Remove gradient_sky
* Remove actual defs for gradient_sky and gradient_primary
* Remove other gradient defs
* Remove gradient support entirely
* Deprecate 'variant' in favor of 'color'
* Fork base styles codepath to make variant deprecation more obvious
* Remove text styles for when no color is set, never been used
* Fork text styles codepath to make variant deprecation more obvious
* Revert temp storybook commit, remove deprecated values
* Replace remaining gradient button usage
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