Add a statsd-exporter instance
The buckets for the histogram mapping are mostly arbitrary for now.
This will enable end-to-end testing of the statsd metric setup.
Depends on !49 (closed).
Test Plan
after a while, prometheus should succeed in scraping the metrics from the statsd exporter (look at http://localhost:5080/prometheus/targets)
Migrated from D1005 (view on Phabricator)