Fix zarith package conflict and add macstadium partnership
type:internal
Macstadium partnership https://tezos-dev.slack.com/archives/GLGGHDDMH/p1648755812247299
Also fix zarith package conflict introduced by : https://github.com/ocaml/opam-repository/commit/97e70c430d3bf970d27e662f5c01b243a19c2984
Edited by Laurent Canis