Upstream issue: https://github.com/istio-ecosystem/sail-operator/issues/1091

Short summary:

The external controlplane setup described here does not work for lbs with DNS names instead of IPs.

As part of this:

• The documentation needs to be updated to support environments with lbs that have either IPs or DNS names.
• Sail Operator needs to be updated to perform readiness checks via URL from the remote --> primary.
• Multi-cluster external controlplane integration tests need to support lbs with either IPs or DNS names.