git walker/drawer - draw relationship between subdatasets

Heavily related to

- #1

as might even be just an option. We often to visualize and navigate heavy collection of subdatasets. We do have handy CLI commands like `datalad subdatasets` but those lack flexible options for limiting (perspective suggestive work is going in

- https://github.com/datalad/datalad/pull/7820

).

I think it all relates to that #1 and having some utility, potentially interactive to navigate such universes of the clones and subdatasets, which in turn quite often are clones of the datasets above (e.g. to facilitate YODA/STAMPED principle of self-containment and ephemeral execution)

Start with the existing `datalad subdatasets` CLI command, related issue #1, and the perspective work in datalad PR #7820. Clarify the intended scope and interaction model first; done would mean a usable way to visualize and navigate relationships among clones and subdatasets.

Written by the indexing model from the issue text.