[dockers] label SONiC Docker with manifest (#5939)

Signed-off-by: Stepan Blyschak stepanb@nvidia.com

This PR is part of SONiC Application Extension

Depends on #5938

- Why I did it
To provide an infrastructure change in order to support SONiC Application Extension feature.

- How I did it
Label every installable SONiC Docker with a minimal required manifest and auto-generate packages.json file based on
installed SONiC images.

- How to verify it
Build an image, execute the following command:

admin@sonic:~$ docker inspect docker-snmp:1.0.0 | jq '.[0].Config.Labels["com.azure.sonic.manifest"]' -r | jq
Cat /var/lib/sonic-package-manager/packages.json file to verify all dockers are listed there.

scripts/j2cli/json_filter.py

@@ -0,0 +1,12 @@
+import json
+
+
+def extra_filters():
+    """ Declare some custom filters.
+
+        Returns: dict(name = function)
+    """
+    return dict(
+        json=json.dumps,
+    )
+