Adopt conda-sphinx-theme

[travishathaway]

Checklist

• I added a descriptive title
• I searched open requests and couldn't find a duplicate

What is the idea?

In order to help ensure a similar look and feel to conda documentation websites, a new theme has been created:

• https://github.com/conda-incubator/conda-sphinx-theme

Although not required to be used by conda projects, it is encouraged. This is issue is my proposal to have conda libmamba solver adopt this theme.

[jaimergp]

I'd love to review a PR if you have the time! If not I'll probably tackle this next week.

[travishathaway]

I'll give it a shot tomorrow. I think this should be a pretty trivial change.

[travishathaway]

@jaimergp,

So the changes were a little more than trivial 😅 , but I hope the docs site is better now. Please check out my open pull request.