Opam support

That means developing:

• 1 lister to actually list opam origins
• 1 loader to actually ingest those listed origins
• actually make those run within the docker dev environment to lift the paper cuts

When that part is done, this implies packaging and deployment work :

• first on staging infrastructure (which will pull the necessary packaging work)
• then deploy it on production

Note that the underlying tool (the opam cli) requires internal state to work (in its OPAMROOT folder). That could pull some more internal work to manage/sync such state to stay consistent between workers (lister and loader).

• [1] http://opam.ocaml.org/doc/Manual.html#opam-root

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Migrated from T3424 (view on Phabricator)