jobs/build-podman-os: set deploy-via-container: true

We implicitly before relied on the osbuild manifest templates to
fall into the `ostree container image deploy` path for our use
case just by having the `container_repo` key set. But a recent cosa
change tweaked this so that now we *must* also explicitly specify
`deploy-via-container`.

See also coreos/coreos-assembler@48f11cc.

Author: jlebon

jobs/build-podman-os.Jenkinsfile

@@ -40,7 +40,8 @@ def generate_diskvar_json(shortcommit, arch, artifacts, staging_repo, repo) {
             "image-type": "${artifact["platform"]}",
             "container-imgref": "ostree-remote-registry:fedora:${repo}:5.1",
             "metal-image-size": "3072",
-            "cloud-image-size": "10240"
+            "cloud-image-size": "10240",
+            "deploy-via-container": "true"
         }
         """
         def file_path="./diskvars-${arch}-${artifact["suffix"]}.json"