[WEB-4683] Docs redesign v2 (holding branch)

[jamiehenson]

A holding branch for all the work outlined here that will be updated as work is completed.

As it stands:

• [x] nav (left, right, header)
• [ ] header
• [ ] footer
• [ ] admonitions & tables

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✨ Finishing touches

🧪 Generate unit tests (beta)

• [ ] Create PR with unit tests
• [ ] Post copyable unit tests in a comment
• [ ] Commit unit tests in branch web-4684-docs-redesign

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