Docs framework - theme switcher updates

[mcoker]

In talking with @andrew-ronaldson let's POC

• An updated "system" icon that conveys something about light/dark/theme stuff.
• Remove the theme toggle text and only show the text in the expanded menu.

Resources:

• https://ux.redhat.com/ - toggle group with cool icons
  
• https://docs.redhat.com/en/documentation/red_hat_advanced_cluster_security_for_kubernetes/4.8#Top%20use%20cases - basically the menu we want to try in a POC.