Support podman as an alternative for docker

[fabasoad]

Problem

Some of the companies restrict usage of docker desktop for macOS and Windows because it is not free (reference). In such cases companies use alternatives such as podman, one of the popular container engine after docker. dependabot requires docker to be installed which makes podman users impossible to use dependabot.

Solution

Add support for podman to enable users use dependabot.

[jeffwidman]

It's a nice idea, but would take some work. The current implementation leverages the docker go libs, so that would need an interface abstraction, and then would need the podman implementation of that interface.

This is open source, so if you're interested in this, please submit a PR. Might be best to first start with an issue outlining your proposed interface abstraction.