Add customConfiguration value for function worker

[acjohnson]

We need the datastax pulsar helm chart to be configurable for the kubernetes runtimeCustomerizerConfig.

So far I have not seen how this is enabled using the helm chart so I've added a customConfiguration value to the function-configmap.yaml template.

This allows us to pass arbitrary configuration to be added to the function-worker(s):

function:
  customConfiguration:
    runtimeCustomizerClassName: "org.apache.pulsar.functions.runtime.kubernetes.BasicKubernetesManifestCustomizer"
    runtimeCustomizerConfig:
      jobNamespace: pulsar
      extractLabels:
        extraLabel: value
      extraAnnotations:
        extraAnnotation: value
      nodeSelectorLabels:
        role: pulsar-functions
      tolerations:
      - key: role
        value: pulsar-functions
        effect: NoSchedule
      resourceRequirements:
        requests:
          cpu: '0.1'
          memory: 128Mi