Helm install should allow WATCH_NAMESPACE to be passed in

[anishakj]

Description
Currently the Helm chart for the zookeeper Operator will ONLY watch for resources in the same namespace that the operator is installed:

    env:
    - name: WATCH_NAMESPACE
      valueFrom:
        fieldRef:
          fieldPath: metadata.namespace

https://github.com/pravega/zookeeper-operator/blob/master/charts/zookeeper-operator/templates/operator.yaml#L27-30

The helm chart should provide a way of overriding this so that the operator can watch ALL namespaces (by passing in "") or another namespace different to the one the operator is installed in.

Location
https://github.com/pravega/zookeeper-operator/blob/master/charts/zookeeper-operator/templates/operator.yaml#L27-30