Add "light-brand" and "dark-brand" colors (add a second color picker) (#2028)

* init dark brand color addition

* added dark mode css vars

* added contrast brand colors

* minor fixes

* added dark branding to loader, button

Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>

packages/prisma/schema.prisma

@@ -142,6 +142,7 @@ model User {
   Schedule            Schedule[]
   webhooks            Webhook[]
   brandColor          String               @default("#292929")
+  darkBrandColor      String               @default("#fafafa")
   // the location where the events will end up
   destinationCalendar DestinationCalendar?
   away                Boolean              @default(false)