@RPCReturnsObservables abstract fun <T> reattachFlowWithClientId(clientId: String): FlowHandleWithClientId<T>?
Reattach to an existing flow that was started with startFlowDynamicWithClientId and has a clientId.
If there is a flow matching the clientId then its result or exception is returned.
When there is no flow matching the clientId then null is returned directly (not a future/FlowHandleWithClientId).
Calling reattachFlowWithClientId after removeClientId with the same clientId will cause the function to return null as the result/exception of the flow will no longer be available.