Dark theme switcher in masthead to use toggle groups

[andrew-ronaldson]

This is an org followup closing design issue #1270

Describe the enhancement
Design team decided to change from the switch component to the toggle group to see both light and dark options.

The new design implementation uses these icons from fontawesome:
Moon - <i class="fa-solid fa-moon"></i>
Sun - <i class="fa-solid fa-sun"></i>

[andrew-ronaldson]

As a followup it would be good to add recommendations to the dark theme docs about using the Toggle group component. Ideally theming should be handled in a products User preferences but if that is not available this option is the preferred solution.