Remap color scheme names to be theme-agnostic in embedding SDK

[heypoom]

Currently we expose the exact colors we are using in the codebase to the SDK: brand, text-dark, text-light and text-medium. The text-* colors currently represent the different tints, where text-dark is darker than text-light.

This is problematic for dark-themed SDK users, as for dark themes those names could have the opposite semantic. We could remap these colors in the publicly-exposed theme configuration so that they're theme agnostic - so they have good meaning in both dark and light themes.

• text-dark to text-primary
• text-medium to text-secondary
• text-light to text-tertiary