Ingest opam instance https://coq.inria.fr/opam/released/

as proposed by mclovin on IRC:

14:21 < mclovin> I was thinking, could we archive one more opam instance ? 14:21 < mclovin> I was thinking of: https://coq.inria.fr/opam/released/ 14:21 < mclovin> the official opam instance is mainly for ocaml packages, but this one contains a lot of Coq related packages

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Migrated from T3717 (view on Phabricator)