Refocus software folder to be about AWS

[sjspielman]

Closes #493

This PR updates the "software platforms" section of the website to instead be focused on AWS. The vast majority of changes here are updating relative links. Here are the other changes:

• I renamed the folder software-platforms -> aws.
  • I named this new section "Cloud storage and compute," since contributors will probably not know what AWS refers to just seeing it in the navbar.
  • I created a nested directory for LSfR docs, and I shortened those page names since the organization now makes it clear that these are LSfR docs. There is no index.md for this nested directory.
• The content in aws/index.md is essentially the same content that was in software-platforms/aws/index.md, which in the diff you will see has been deleted.
• I updated mkdocs.yml accordingly

[sjspielman]

Hm, why didn't 0.3.0 spellcheck kick in? We have the v0 tag and the most recent version was indeed pushed... https://github.com/AlexsLemonade/spellcheck/pkgs/container/spellcheck CC @jashapiro