Publicly expose the current FLR and SLR count

[mauroservienti]

As a user I want to able, from the code running in my handler, to retrieve the current retry count (both of FLR and SLR) and the max retry so to determine how to behave if the current retry is the last one.

Basically as a user I want to know something like: this is the last attempt, if it fails the message will be delivered to the error queue.

An amazing approach would be if this can be handled using the pipeline:

class Interceptor : IFailedMessageHandler<MyMessageType>
��{
    void Handle( ... ) // this is called just before sending the message to the error queue
}

[dannycohen]

Somewhat related to Particular/ServiceControl#65

[mauroservienti]

You da man!

[SimonCropp]

duplicate of #2473