Add ability to attach additional labels to NiFi pods

[mh013370]

Feature Request

Is your feature request related to a problem? Please describe. No.

Describe the solution you'd like to see I'd like to attach arbitrary labels to pods that nifikop creates. Specifically, i'd like to label pods with meaningful things as a means to select pods for log aggregation via https://rancher.com/docs/rancher/v2.6/en/logging/

For example:

apiVersion: nifi.orange.com/v1alpha1
kind: NifiCluster
metadata:
  name: simplenifi
spec:
  ...
  pod:
    labels:
      specific-pod-label: "abc"
  nodeConfigGroup:
    default_group:
      nodeLabels:
        my-special-label: "true"
  ...

Describe alternatives you've considered Annotations can't be used as pod selectors and the only labels applied to the pods nifikop creates match the name of the NiFiCluster CRD under the label nifi_cr. Otherwise, there's not a label that distinguishes multiple nifi clusters deployed by nifikop.