Support ssh key in building images

[dfn-certling]

Is your feature request related to a problem? Please describe.
podman-compose does not seem to support the ssh key as part of the build specification for images (https://github.com/compose-spec/compose-spec/blob/master/build.md#ssh).

Describe the solution you'd like
Supporting the ssh key should boil down to an addition to build_one along the lines of

    for agent_or_key in build_desc.get("ssh", []):
        build_args.extend(["--ssh", agent_or_key])

That should extend the arguments provided to podman build to include the proper key or agent socket. I can prepare a pull request if this is interesting.

Describe alternatives you've considered
It is possible to provide keys on a global level by adding something like --podman-build-args \\--ssh=default, but that needs to be added explicitly and does not easily allow to use different keys or agents for different images.

[2ToTheNthPower]

I second this. I haven't found a way to build the way I want without this feature, so I've had to use docker compose.

[mladedav]

I also believe that this should be available without workarounds. However, if you need just single agent, you can use what dfn-certling has already suggested: --podman-build-args \\--ssh=default