Build docker image for pipeline cron service

Build `kernelci` image with `pipeline-cron`
fragment. This image is used for pipeline
cron service.

Signed-off-by: Jeny Sadadia <jeny.sadadia@collabora.com>

Author: Jeny Sadadia

.github/workflows/docker_images.yml

@@ -111,6 +111,7 @@ jobs:
                   'kernelci',
                   'kernelci api',
                   'kernelci pipeline',
+                  'kernelci pipeline-cron',
                   'kernelci lava-callback',
                   'k8s kernelci',
                   'qemu',