A few reasons. First of all, it doesn't require a running Docker daemon
instead outputting directly to a file (faster and saves space). Also,
the restore script will probably use skopeo so this the codebase is more
uniform. Without the Docker daemon it can run with lower privileges.
Lastly, it should work without setting the really high timeout that bugs
me a little.

Meant to be run on a different machine. It can be used on the same
machine and then the resulting files can be copied over.

I only have off-site backups for host01. In case I need to rebuild ns4
or rebuild shore.co.il infrastructure I need those images (although I
can probably build them locally and push them, it's probably easier and
faster to restore from backups). So this commit includes:

- Empty Python script.
- pre-commit hooks for Python.
- Dockerfile for the image (with the requirements and script).
- GitLab CI job for backup on host01 (bind mount the dockerd socket and
  /var/backups) and a notification job in case the backup fails.

All that's left is to write the backup script.