Docker: Install Opam 2.2 from Alpine Edge repository

Listen, I haven’t chosen this. It is not my fault if our dependency tree now requires us to have Opam 2.2 installed. Blame the most recent version of ocaml-env-msvc32.1 (I think). Me? I just want to enjoy the latest version of ocaml-lsp-server. Which is not part of the opam repository hash we are relying on today.

Anyway, fortunately, Opam 2.2 is already packages for Alpine, in the so-called Edge repository. I guess this means Opam 2.2 will be part of the next Alpine release, but considering Alpine 3.20 is a few weeks old, I propose to take a shortcut in the meantime and install Opam from the Edge repository.

You can argue ocaml-lsp-server is a shallow reason to do such a thing, but the next time we need to upgrade an external dependency in a hurry, you might be happy to not have to deal with Opam 2.2. Not to say the stuggle is completely over. We are still inhereting from a conflict in our dependency tree. But at least, Opam is no longer an issue.

Manually testing the MR

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