dr/ldr: support node to LB setup 

Some users may want to run LDR through a load balancer. This is not recommended because it impairs performance, but can be a needed workaround under some network topologies.

Users who want to do this should use the load balancer address as the SQL advertised address on each cluster.

This is for CRDB 24.3.

Jira issue: DOC-11073

Epic CRDB-40896