git walker/drawer - add ability to discover, "pre-view" and add as remote clone

Sources could be the

- github "Insights" -> "Network"
- https://registry.datalad.org/ ( e.g. based on dataset UUID)
- ...

then in the preview of "Other forks" would be great to be able to gather stats to visualize similar to #5 , and potentially even giving optionally ability to draw the DAG of "advances" of those clones past current state, and ability to "Add" any found clone as a remote and thus become part of this navigatable DAG across clones. By default, clones without new commits past state of original repo should be "greyed out".

Start by reviewing GitHub Insights → Network and the registry.datalad.org example based on a dataset UUID, then compare the requested preview and statistics with issue #5. Done means discovered forks or clones can be previewed, relevant DAG advances can be visualized, and a selected clone can be added as a remote while unchanged clones are greyed out.

Written by the indexing model from the issue text.