Field k8s_audit_level is null when pruned the field structured.level in RHOCP 4

Issue

• Prune option in not working as expected
• k8s_audit_level has always "null" value

• Tried using prune filter with the following configuration, but the k8s_audit_level value is always null

    - name: prune-filter
      prune:
        notIn:
        - .log_source
        - .log_type
        - .message
        - ."@timestamp"
        - .k8s_audit_level