Update Note to Balloters text to guidance and change heading from "Reliable Delivery" to "Server Response Codes"

Existing Wording:

Reliable Delivery
Upon receiving a message, the Receiver/Intermediary may return one of several status codes which is documented in $process-message definition.
....
At the Dec 11-12 Da Vinci Connectathon we polled the participants and determined that the following codes and guidance could be added:

200,202,204+/- OperationOutcome all ok for successful transactions
Issue : what does widely use Java client want?
401,404+/- OperationOutcome no point in retry
429 +/- OperationOutcome retry but slow down traffic
500+ +/- OperationOutcome - server issues may retry a few times

Proposed Wording:

Server Response Codes

Upon receiving a message, the Receiver/Intermediary may return one of several status codes which is documented in $process-message definition.For this implementation, for successful ~$process-message transactions any one of`200`,`202`,`204` (+/- OperationOutcome) *MAY* be used. The following table defines the Sender behavior for the following error codes: