Automate CLI / func docs generation

[abrennan89]

Describe the change you'd like to see
The options for kn and func CLI commands are constantly being expanded and updated.
It is not reasonable for docs to be manually updated frequently enough to keep up with the changes.
I would like to see folks on the eng team provide some method of implementation for auto-generating docs reference pages for the CLI tools that can be published on the website.

Additional context
Previously discussed with @rhuss for kn and with @lance for func implementation after KubeCon (Oct 2022).

[psschwei]

Also some discussion in #4430