PollingSubscriberConnection - allow number of messages delivered to be configurable

The value is hard coded to an upper bound of 1000 (which used to be 500). Shouldn't it be configurable?

This doesn't work well for really large messages and for messages that take substantial time to process.

I see no way to configure this value. Doesn't look like the client has any control over the number of messages pulled from the subscription. I was hoping that the FlowController logic would support but it seems focused on whether/when to go back the server to get more rather than limiting the number pulled.

Note that if FlowController is set to 1 element, deadlock is likely on the FlowController semaphore (for example, it being set to 1, while having just processed 10 messages).