idempotentInvocationHandle  
  open fun <Res> idempotentInvocationHandle(target: Target, idempotencyKey: String, resTypeTag: TypeTag<Res>): Client.IdempotentInvocationHandle<Res>
Create a new IdempotentInvocationHandle for the provided target and idempotency key.
Return
the idempotent invocation handle
Parameters
target
the target service/method
idempotencyKey 
the idempotency key
resTypeTag  
type tag used to deserialize the invocation result