docs: use mike for multiple docs versions on website

[kelly-sovacool]

Changes

Configures the docs site + github action to host multiple versions

One-time set up steps:

• delete all files in gh-pages, commit this
• check out the previous release tag and run mike deploy 2.5 latest -push --update-aliases --branch gh-pages
• set the default landing page: mike set-default latest
• from the main/dev branch, run mike deploy dev --push --update-aliases --branch gh-pages

After this is merged into main, from then on the dev version will be updated automatically when new commits are merged into main, and the latest version will automatically be set to the latest release.

Issues

resolves #97

PR Checklist

(Strikethrough any points that are not applicable.)

• This comment contains a description of changes with justifications, with any relevant issues linked.
• Update docs if there are any API changes.
• Update CHANGELOG.md with a short description of any user-facing changes and reference the PR number. Guidelines: https://keepachangelog.com/en/1.1.0/