Move some manager client RPCs to assistant managers

[keith-turner]

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