distro/rhel-9: set podman default network backend to netavark

RHEL 9 Podman falls back to the legacy 'cni' network backend when it
finds pre-existing container images in storage, but the 'cni' packages
are not installed by default. Force 'netavark' so that images with
embedded containers work out of the box.

This only affects RHEL 9 / CentOS Stream 9; newer distros (and newer
podman versions) don't have this fallback logic.

Regenerate test manifests. All el9 / c9s manifests that embed
containers now get the podman default network backend set.

Signed-off-by: Tomáš Hozza <thozza@redhat.com>

Author: thozza

data/distrodefs/rhel.yaml

@@ -220,6 +220,7 @@ distros:
     image_config:
       default:
         default_kernel: "kernel"
+        podman_default_net_backend: "netavark"
         default_oscap_datastream: "/usr/share/xml/scap/ssg/content/ssg-rhel9-ds.xml"
         install_weak_deps: true
         locale: "C.UTF-8"