docs: expand base template and improve descriptions

[jsstevenson]

This PR covers a few documentation-related aspirations

• Iterates on what I'd propose for the "Wagner lab template". Employs a new theme, Furo, which I think looks better. Adds some new Sphinx plugins and tries to use better ReST.
• Adds a live graph figure to the normalization page, and provides a script to generate it. I haven't incorporated this into the Makefile since it's one script but that could be done if the scripts directory grows.
• Small documentation tweaks to improve API descriptions
• Updates OpenAPI stuff. We were previously using a bit of an indirect way to define some metadata.
• Added a tests and min. python version badge

Also we can close #185, close #206

A few discussion points/possible todo's:

• The Furo theme is pretty easily customizable (a big reason why I think we should stick with Sphinx instead of moving over to Mkdocs, even though I really like the Material mkdocs theme). I haven't altered the default colors here but we could definitely put together a lab theme (@katiestahl ?) at some point. We also need to figure out a way to alter the figure's CSS.
• It'd be great to incorporate some of @anastasiasmith1221's work on gene terms as it develops: for example, in a "recipes/cookbook" type section (i.e., here's an example of some code using the gene normalizer to do a big analysis project), and/or in a "here is the problem" section (i.e. here are examples of ambiguities in references that lend themselves to normalization)
• I wanted to do a short blurb on VRS somewhere if it seemed relevant
• I would prefer that subsection indexes don't exist but I'm not sure if I can turn this off
• Mention difference between 0.1.x and 0.2.x

btw, PRs should now trigger new readthedocs builds, so you can check out how this would look here: https://gene-normalizer--209.org.readthedocs.build/en/209/

[korikuzma]

@jsstevenson what's the priority on this PR?

[jsstevenson]

@korikuzma very low

[jsstevenson]

I think it might make more sense to move the Gene record summary over to this page, and put GeneDescriptor on the normalization page

[korikuzma]

Or even having sections for search, normalize, and normalize_unmerge?

[korikuzma]

Only requesting change for the seqrepo path because I think it was a typo. This is coming together quite nicely! I do agree it would be nice to have a little section about VRS and how we support different versions

[korikuzma]

I know it's not part of this issue, but you can remove the requirements in this PR if you want. Or we can do it in a separate issue

[korikuzma]

Or even having sections for search, normalize, and normalize_unmerge?