multi-tenant: Enhanced DistSQL separate-process MR clusters

In non-multi-tenant multi-region clusters, DistSQL will try to route requests to the local node if a suitable replica exists there. In multi-tenancy we don't currently take advantage of this optimization.

The ability to do so for shared-process multi-tenancy is tracked in #109522. For separate-process multi-tenancy however, the optimization is trickier to implement, as we'd need to determine if the given SQL pod is co-located with a KV node which contains a suitable replica. While tricky to implement, this enhancement has the potential to provide a significant performance impact over the current approach where nodes in the same locality (region/zone) are favoured.

Jira issue: CRDB-31581
Epic: CRDB-10360