Add documentation to Infix image for CLI/Web

[troglobit]

• Include all documentation in the image
• Add CLI keywords man and apropos (alias search maybe?)
• Allow bringing up and searching from anywhere in the CLI

admin@example:/config/interface/eth0/ipv4/> search ipv4ll
networking: Setting up IPv4 link-local address
...

[troglobit]

Looks like https://www.sphinx-doc.org/ may be the best alternative to tie it all together with. It can read both traditional .rst (restructured text) format and .md (commonmark format with lots of extensions), meaning we write the glue logic in .rst files and keep all existing .md files as-is.

Possibly we should move to .rst for test documentation as well.

[troglobit]

Another, very interesting, alternative is Material for MkDocs, which aims to always be compatible with GHFM (GitHub Flavored Markdown). Meaning, we can retain the current "just works" browsing of documentation via the GitHub interface, and from the same sources generate documentation for multiple targets.