Update docs structure for website versioning improvements

[thomas-bc]

Related Issue(s)
Has Unit Tests (y/n)
Documentation Included (y/n)

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Change Description

Updating docs structure and mkdocs.yml a lot. This comes with the following improvements

• Top level contents are not being versioned anymore (e.g. https://fprime.jpl.nasa.gov/events which could cause lots of confusion if old versions of it were still being shown)
• Versioning is restricted to the source/docs folders
• Entire fprime/ folder is being hosted on the website, major improvement in cross-linking capability (all relative links within the repo resolve correctly on the website, for example in SDDs linking to other docs).
• Other misc improvements, such as adding a "Display source" button on each page that will take you to the source on the website.

Testing/Review Recommendations

These changes are currently live on https://fprime.jpl.nasa.gov

Future Work

Re-establish internal CI which was disabled while testing this

[LeStarch]

LGTM.