add images command for additionalimagestore

[lastephey]

Should address #87

Instead of adding and then removing additionalimagestore from the defaults, I just created a separate images command. I thought this would be a cleaner way to handle the problem.

Have done some basic testing in a muller reservation and standard behavior (pull, build, run) seems ok.

stephey@nid001003:/mscratch/sd/s/stephey/podman-hpc/podman_hpc> podman-hpc images
REPOSITORY                TAG         IMAGE ID      CREATED         SIZE        R/O
localhost/test            test        b0bfc82c60de  12 minutes ago  550 MB      false
localhost/test            test1       841451f9dbb7  8 days ago      80.4 MB     true
localhost/test            test        61b85dc0093d  8 days ago      550 MB      true
docker.io/library/ubuntu  latest      c6b84b685f35  6 weeks ago     80.4 MB     false
docker.io/library/ubuntu  latest      c6b84b685f35  6 weeks ago     80.4 MB     true
docker.io/library/ubuntu  focal       6df894023726  8 weeks ago     75.2 MB     false
docker.io/library/ubuntu  focal       6df894023726  8 weeks ago     75.2 MB     true

[danfulton]

Seems like a clean solution to me.