Add unprocessable event policy on consumption

[a1exsh]

This allows the user to choose between the current implementation of skipping the unprocessable events, or sending those events to the dead letter queue.

[a1exsh]

One other thing to take care of is, either to have this dlq event type created or somehow disallow DEAD_LETTER_QUEUE policy now.

Right, this remains to be followed-up on. I tend to keep the policy allowed even if the event type is not present — that's not harmful, as long as no one actually depends on it working.

[samizzy]

:+1:

[a1exsh]

@samizzy @1u0 I've included the DLQ store event type definition in the app resources — that enables local testing and makes the code shorter as well. Please have another look.

[samizzy]

:+1:

[a1exsh]

:+1: