[FEATURE] Provide an example of HA client configuration

[yuri1969]

Is your feature request related to a problem?

During an OpenSearch cluster upgrade the client might go unresponsive from various low-level reasons - cache ignoring the DNS switch, opened TCP connections becoming stale for long time, etc.

This is a problem mainly in HA environments.

What solution would you like?

Adding a "HA config" example snippet to Java client | OpenSearch Documentation

What alternatives have you considered?

Creating a minimal working code example directly in the repo.

Do you have any additional context?

Apache HC5 provides a vast array of low-level configuration options but having an official recommendation would make things clear.