v2.3.0-rc13: Fetch replicaset from etcd if not found in cache

During workload rollback, for deployments under apps/v1, we need to get
replicaset spec.
The rollback handler was getting replicaset from cache, but for HA setups
sometimes the replicaset wasn't getting returned from cache.
This commit adds fallback logic to fetch the replicaset from etcd if fetching
from cache fails