[Recovery] Introduce fatal errors

[lovromazgon]

We need a specific error type so the recovery mechanism will be able to detect which errors are fatal and which ones can be retried.

A fatal error should be returned in the processor node to signal that a processor nacking a record is a fatal error, as well as in the DLQ when the nack threshold is reached and the nack threshold is more than 0.

It should be possible to convert any existing error into a fatal error, for example:

err := foo()
if err != nil {
	return cerrors.FatalError(err)
}

The fatal error should implement Unwrap() error so that the wrapped error can be accessed. We should also provide a convenience function to check if it's a fatal error like cerrors.IsFatalError(err).