Add versioned documentation

Setup mike to provide versioned builds of the documentation.

The goal is to have versioned docs for stable releases (0.23.0, 0.24.0)
and development docs that can progress along with the code. This allows
us to tailor docs to the next upcoming version as we no longer need to
care about diversion between rendered docs and the latest release.

Versions:
* development (alias: unstable) on each push to the main branch
* MAJOR.MINOR.PATCH (alias: stable, latest for the newest version)
  * for each "final" release tag
  * for each push to doc maintenance branches: doc/MAJOR.MINOR.PATCH

The default version should the current stable version. The doc
maintenance branches may be used to update the version specific
documentation when issues arise after a release.

mkdocs.yml

@@ -71,6 +71,7 @@ plugins:
   - include-markdown:
   - minify:
       minify_html: true
+  - mike:
   - social: {}
   - redirects:
       redirect_maps:
@@ -90,6 +91,9 @@ plugins:
 
 # Customization
 extra:
+  version:
+    alias: true
+    provider: mike
   annotate:
     json: [.s2]
   social: