Fluent DSL. Expect subscription followed by immediate stream completion. By default single demand will be signaled in order to wake up a possibly lazy upstream

Fluent DSL. Expect subscription followed by immediate stream completion. Depending on the `signalDemand` parameter demand may be signaled immediately after obtaining the subscription in order to wake up a possibly lazy upstream. You can disable this by setting the `signalDemand` parameter to `false`.