Add the notion of a "service container" to play kube. A service
container is started before the pods in play kube and is (reverse)
linked to them. The service container is stopped/removed *after*
all pods it is associated with are stopped/removed.
In other words, a service container tracks the entire life cycle
of a service started via `podman play kube`. This is required to
enable `play kube` in a systemd unit file.
The service container is only used when the `--service-container`
flag is set on the CLI. This flag has been marked as hidden as it
is not meant to be used outside the context of `play kube`. It is
further not supported on the remote client.
The wiring with systemd will be done in a later commit.
Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>
Valentin Rothberg