Text colors should follow the background based on color contrast in embedding SDK

[heypoom]

We should provide support for both light-theme and dark-theme users of the sdk by providing automatic contrast detection. The idea is that foreground color should follow the background color defined in #42678 by detecting whether the background is dark or light mode.

[heypoom]

Closing this issue as we already provide text-primary, text-secondary and text-tertiary settings that the user can control. Refer to the discussion here.