Add stagit lister

It's a cgit/gitweb like technology

"stagit is a static page generator for git." [1]

Instances example [2]

Plan:

swh/devel/swh-lister!486 (merged): Implementation
swh/devel/swh-environment!273 (merged): List various instances in docker (see mr description)
Deploy in staging
Deploy in production
(ongoing) Ingest forges [2]
swh/devel/swh-web!1161 (merged): Reference in archive coverage widget and add type to add-forge-now ui

[1] https://codemadness.org/stagit.html

[2] (Thx @guillaume for the listing again ;)

Edited Jul 28, 2023 by Antoine R. Dumont

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