Make ES replica sets part of the tenant configuration

[txau]

We are currently hard-coding the amount of ES replicas to 0. This happens as the default ES configuration and during the re-index process.

In order to speed up re-indexing operations, we set the replicas to 0, and when we restore the index configuration after the reindex, we hard-code it to 0 again.

Because we want to be able to load balance ES for some tenants, but not for all of them, we need to make this param configurable as part of the tenant config.