Automate CLI docs in our sphinx docs to avoid manual and duplicate specification

ATM manually curated, duplicating work/docs in click specifications and under `docs/`.

Initial attempt to automate was via sphinx-click in https://github.com/dandi/dandi-cli/pull/831 but there were shortcomings at that point.

@satra also suggested https://github.com/jdidion/autoclick in https://github.com/dandi/dandi-cli/pull/1001#discussion_r865961200 so (I guess) docstrings (not really CLI --options etc) are displayed as is, and then CLI interfaces are produced. Not sure if that is not "too ad-hoc/heavy".

So may be sphinx-click should be reconsidered or some other approach developed.