Issue 3529 metrics to piggybank

@shane-tomlinson Could I get your feedback on this? Not sure it's ready, but maybe it is (might also need to wait for privacy review before merging, I'm not sure).

This is a fix for mozilla/identity-ops#102 that sends some additional RP metrics to kpiggybank along with the existing kpi data. We do this by extracting the `wsapi/interaction_data` kpi code into a separate lib, and dropping a few additional logger calls into `bin/verifier` and `bin/router`.

There is a separate privacy bug open for collecting the RP metrics, and there's also a ton of related conversation, inside mozilla/identity-ops#102.

Open questions:
* what format should I use for the new data? what should I call the keys, how should I namespace them?
* do we need to wait until privacy review is done to merge in? 
* are there other metrics I should fold into this PR? I'm thinking particularly of #3755.