Cli docs

This adds a reference documentation for https://dev.funkwhale.audio/funkwhale/cli/, as well as some usage examples.

cc @Sporiff, you can view the result here: http://funkwhale.pages.funkwhale.audio/-/funkwhale/-/jobs/27329/artifacts/docs-review/cli/index.html

(I've cherry picked some commits some develop so we can have online review of the documentation)