Support for distrobox

[lfromanini]

This is more an enhancement than an issue.

When using Distrobox, our home folder is mounted within a container (podman or docker). Using the command distrobox enter <container_name> we can't see any difference from shell prompt and it's hard to know if we are on the host or inside the container.

My proposal is to have the hostname and a flag indicating if we are in the container. This can be made with this hack in the ~/.zshrc:

if [[ -e /.dockerenv ]] ; then
    psvar[1]="@${(%):-%m} «Docker»"     # show hostname inside docker containers
elif [[ -e /run/.containerenv ]] ; then
    psvar[1]="@${(%):-%m} «Podman»"     # show hostname inside podman containers
fi

However, it will be better if this was merged in the source code. Additionally, would be nice to have a way to overwrite the colour of "Docker" and "Podman" words. Suggestion: AGKOZAK_COLORS_CONTAINERENV.