Add docker compose setup and integration test with 3 rest-catalog instances and etcd cluster(3)

[subkanthi]

• Add docker compose setup and integration test with 3 rest-catalog instances and etcd cluster(3)
• Document the steps to migrate from 1 node etcd cluster to 3 nodes in k8s.

https://github.com/Altinity/ice/blob/backend_data_documentation/docs/etcd-cluster-setup.md

Steps applied :
Scaled etcd pods to 0
Updated ConfigMap -> initial-cluster-state":"existing"
‘uri’ & ‘ETCD_INITIAL_CLUSTER’ values as expected (printed in logs)
Scaled etcd pods to 3 (2nd pod resulted in error, logs attached)