Move some manager client RPCs to assistant managers

**Is your feature request related to a problem? Please describe.**

The primary manager process handles all client RPC. Some of these RPCs could be handled by any manager process.

**Describe the solution you'd like**

* Create a new thrift service, could call it AssistantManagerClientService
* Move any RPCs that can move from ManagerClientService to AssistantManagerClientService
* Rename ManagerClientService to PrimaryManagerClientService
* Update client code to call the appropriate service.

Similar changes where made in #3262, but the code has changed a lot since then. Can reference the client changes made in that PR.

**Additional context**

This is a follow on issue to #6168