Description of problem:

Fields kubernetes_container_name, kubernetes_namespace_name, kubernetes_pod_name not getting pruned for loki output even after applying prun filter

Version-Release number of selected component (if applicable):

Logging 6.3

How reproducible:

Always

Steps to Reproduce:

1> Install Logging with loki stack

2> Try Filter [A]or  [B]. 

[A]

  - name: remove-pod-owner2
    prune:
      notIn:
      - .log_type
      - .message
      - .log_source 

[B]

  - name: prune-filter
    prune:
      in:
      - .kubernetes.container_name
      - .kubernetes.container.name
      - .kubernetes_container_name
      - .kubernetes_container.name
      - .kubernetes_namespace_name
      - .kubernetes.namespace_name
      - .kubernetes.namespace.name
      - .kubernetes_namespace.name
      - .kubernetes.pod_name
      - .kubernetes.pod.name
      - .kubernetes_pod_name
      - .kubernetes_pod.name 

Actual results:

kubernetes_container_name, kubernetes_namespace_name, kubernetes_pod_name not pruned

Expected results:

Fileds kubernetes_container_name, kubernetes_namespace_name, kubernetes_pod_name should be pruned or they should be listed as non-prunable fileds in doc

https://docs.redhat.com/en/documentation/red_hat_openshift_logging/6.3/html/configuring_logging/configuring-log-forwarding#logging-content-filter-prune-records_configuring-log-forwarding

Additional info:

For audit logs where no values are there for 

kubernetes_container_name, kubernetes_namespace_name, kubernetes_pod_name they are blank still there and not prunable

NOTE Please see attched images to get clarity on issue