add to archive coverage page a breakdown of the number of origins per lister [instance]

Now that the amount of origins other than major forges is increasing and diversifying, it would be nice to have a breakdown that shows how many origins we have coming from GitHub, how many from each GitLab instance, etc.

The mental model is a piechart showing a breakdown, but the visual might be different

This is related to #1870 (closed), and the underlying automation will probably be the same.

Migrated from T2468 (view on Phabricator)

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