make RabbitmqProducer using TopicInterpolator generate rounting key

[eshizhan]

This commit make RabbitmqProducer using TopicInterpolator. It is designed to use a unified logic, and additionally supports type substitution as a routing key.
P.S. also add metrics and error logging for RabbitmqProducer

[osheroff]

cool, but if I merge this I break all the installations that are currently using the %db% format. Please make this PR backwards compatible.

[eshizhan]

@osheroff added backward compatibility.

[osheroff]

ok great. can you add a test around the behavior then I'll merge? Sorry our producers are way undertested

[eshizhan]

I didn't find any existing test code for RabbitmqProducer, and I'm not familiar with the relevant test methods. I'm very sorry that I haven't had much energy to build a new test case recently. However, I have already deployed it and verified it for this PR.

[eshizhan]

@osheroff Added metrics and error logging for RabbitmqProducer in this PR. The TODO commented code about ignoreProducerError will change the previous default behavior. I think it is up to you to decide how to handle it. Thanks for review!