Set a default producer-window-size on cluster connection

The current producer-window-size configuration for cluster connection is -1 ie unbounded: it means that in case of an intermittent slow network or scarce CPU resource on the receiving cluster node (due to GC activity, OOM or other reasons) both brokers risk to go OOM:

• the sender one because of the resend cache on the channel of the cluster connection (still present because of confirmation window size defaulted to 1 MB): unbounded granted credits means that it could grow unbounded while containing the clustered packets awaiting to get response or confirmation from the other node (that could be busy/overloaded and unable to answer anything back)
• the receiver one due to the Actor abstraction on the cluster connection: the sender would try to send as much packets it can, regardless the ability of the receiver to consume them, that would accumulated on the actor mailbox (that's unbounded) instead of the TCP buffer (that's bounded)