Add theme prop to switch between light and dark mode

[shanedaugherty]

Is your feature request related to a problem? Please describe.

When my site is loaded in dark mode the Disqus component shows in light mode

Describe the solution you'd like

A theme override prop would solve my problem

Describe alternatives you've considered

N/A

[surdu]

Actually, in my case is worst than this: if I set in my css the color-theme property to color-scheme: dark;, the whole Disqus section uses the light mode, and vice-versa ...

Maybe the simplest solution is for the Disquss widget to honor color-theme properly