docs: restructure docs by version

[janechu]

Currently the docs site builds all 3 versions as subpaths each time from a single build process, the build time will get worse as more docs are added.

Structural Update Requirements

• Split each major version into 3 separate private packages in the sites folder
• Use the website folder to hold any common items necessary and build scripts
• The change should be able leverage the current use of lage to only build docs that have changed
• These should still be available on the 1.x, 2.x, 3.x, etc., subpaths