Support Podman instead of Docker

[dmcc]

We've received feedback that Podman doesn't require root while Docker does. This makes Podman more suitable for some computing environments (e.g., HPC).

[dmcc]

@drewp tested with Podman and ran into this issue:

% pdm go                  
[09:51:48] Running 'docker buildx build --ssh=default=$SSH_AUTH_SOCK --build-context project=. --quiet --tag 08fd0e2 https://github.com/quant-aq/aeromancy.git#v0.1.0:docker'                                  runner.py:118
[09:51:49] Docker output: Emulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.                                                                                                       runner.py:121
           Error: prepping temporary context directory: cloning "https://github.com/quant-aq/aeromancy.git#v0.1.0:docker" to "/var/tmp/buildah1050619706":                                                                  
           error: pathspec 'v0.1.0' did not match any file(s) known to git                                                                                                                                                  
           : failed while performing git checkout: exit status 1                                                                                                                                                          
Docker exited with 125

Our understanding is that Podman doesn't actually accept Git URLs like https://github.com/quant-aq/aeromancy.git#v0.1.0:docker (but needs further investigation).