Updates from review of V2 docs

[pjbull]

Per the comments, does the following:

• Lists packages for "basic" option (needed some refactoring to get those at docs render time)
• Have headers same width as body text
• Add link to announcement blog post at top of docs
• Update tree output at end of index page
• Update opinion pages formatting to be less varied
• Add DD footer to nav links
• Sets min Python version to 3.8
• Add miniconda, which was removed from MacOS images (see https://github.com/actions/runner-images/issues/9262 )

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