fix: Update zookeeper-operator defaults for zookeeper image.

[kaiwalyajoshi]

Change log description

When a Zookeeper Cluster is created, it uses the upstream pravega/zookeeper:0.2.15 image which has known vulnerabilities.

This PR changes the default for the operator to use the patched ghcr.io/mesosphere/zookeeper:0.2.15-d2iq image.

The defaults proposed here can still be overridden via the following when ZookeeperClusters are created:

apiVersion: "zookeeper.pravega.io/v1beta1"
kind: "ZookeeperCluster"
metadata:
  name: "example"
spec:
  replicas: 3        
  image:
    repository: ghcr.io/mesosphere/zookeeper
    tag: 0.2.15-d2iq

Purpose of the change

(e.g., Fixes #666, Closes #1234)

What the code does

(Detailed description of the code changes)

How to verify it

(Steps to verify that the changes are effective)