Support retrying on a different cluster

Retry producer can be configured to use a different cluster but retry consumer cannot. (shares the consumer with the original one)

While this is saves resources in most cases, it prevents enabling retry feature on a cluster you can't freely create topics on.

Start by locating the retry producer and retry consumer configuration in the Java code, then compare how each selects its cluster. Trace the consumer-sharing behavior described in the issue and determine the expected configuration for a separate retry cluster. Done means retry consumers can use a different cluster without requiring unrestricted topic creation on the original cluster, with coverage for both configurations.

Written by the indexing model from the issue text.