Add ArgsEscaped field to image config

[kevpar]

This PR is an attempt to fix containerd/containerd#5067, which currently prevents certain Docker-built Windows images from working in containerd. See the containerd issue for full details. Brief overview below.

Docker has been relying on the unofficial ArgsEscaped field in the image config for several years now. It is added when a Windows image is built using a "shell form" ENTRYPOINT/CMD in the Dockerfile, and indicates that the first element of the Entrypoint/Cmd field contains a full command line, rather than just a path to a binary.

This change was made in Docker to improve support for Windows containers, given differences in how Windows and Linux handle command line args and escaping. Given that there are existing images in the world that rely on this field being set, the easiest way to address the problem appears to be simply adding ArgsEscaped officially to the image spec.

For context, this is how ArgsEscaped is represented in Docker's image config type: https://github.com/moby/moby/blob/46cdcd206c56172b95ba5c77b827a722dab426c5/api/types/container/config.go#L57

[kevpar]

After some internal discussion, going to look into another option for fixing this. Might re-open this in the future if that doesn't pan out.

[jterry75]

@kevpar - Can we revisit this? Were there any objections from OCI to adding ArgsEscaped to the config spec here? It doesn't seem harmful to add given that Docker (/Buildkit) support ArgsEscaped and are the largest producer of images. It's easy to document that ArgsEscaped==true means that the EntryPoint is a pre-escaped single entry array and should not be additionally escaped. Additionally, we already have a provision in the Runtime spec for CommandLine rather than Args specifically to address this issue on Windows. It seems reasonable to have this IMO and then I can make the change to containerd to support it natively. Thoughts?

[estesp]

Seems with the suggestion of using this in containerd via containerd/containerd#6479 we should re-open this for consideration?