Use GID from config for container

[NoahvdAa]

The wings config file has an option for specifying the GID, but it doesn't seem to be used in the container. This PR aims to fix that by passing the configured gid to the container config. This seems to do the job, as shown in the highly advanced tests below /s

Before:

After:

[parkervcp]

The user is to identify outside the container what user is used to own the files. Matching in the container is probably a good idea.

We should probably update the yolks and images to actually use 997 to make the container user before this gets implemented though.

[DaneEveritt]

No, because 997 is not the guaranteed ID of the user, the host can change it. We can pass the group through, just need to confirm it didn't break any existing images. I don't agree with making a user in the container.