Defaults for Podman that were previous applied as command-line arguments
to all `podman run` or `podman create` invocations are now specified in
a dedicated configuration file.
Services are also better identified against their name rather than the
generic `podman` ID derived from the `ExecStart` invocations.
This commit implements three new services, specifically:
- The `container-volume` service, which applies to a specific volume
name and ensures this exists. This is mainly useful as a dependency
to other services, as Podman will create named volumes itself if
needed.
- The `container-volume-backup` service, which creates a `tar.gz`
snapshot of the given volume's contents in `/var/lib/backups`.
- The `container-volume-restore` service, which populates an empty
volume from a pre-existing file in `/var/lib/backups`, presumably
created by `container-volume-backup`.
These are then be used to automatically create volume snapshots every 12
hours, rolling over every 7 days.
