[xCluster] Make xCluster work in Kubernetes

[ndeodhar]

Jira Link: DB-7176
There are 2 changes needed to get 2DC to work:

1. SetupUniverseReplication should accept a load balancer IP. This will be the host that all CDC service GetChanges requests are routed to, instead of routing them to individual tablet servers.

2. Similarly, while setting up UniverseReplication, we currently provide a list of producer master addresses. Since we need to get that to work with a load balancer, we need to add a wrapper SetupUniverseReplication in CDCService. Then yb-admin SetupUniverseReplication will call tserver's SetupUniverseReplication via load balancer host and then that should then route the call to master leader's SetupUniverseReplication.