Tezt_cloud: Add macosx dockerfile

What

Parent MR: !16078 (merged)

This MR adds a working dockerfile for testing the tezt-cloud scenarios for macOS users.

Why

So that macOS users can bring more involving contributions to the tezt-cloud code stack. 😃

How

Manually testing the MR

Try the following:

$ dune exec tezt/tests/cloud/main.exe -- cloud dal --localhost -v --tezt-cloud macosx --macosx --vms-limit 2 --binaries-path /build/tezos --no-check-file-consistency

This should not be stopped by any error. You can stop it after a few levels, as it goes on indefinitely.

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR