bucket to data set

Breaks collectors, review and merge with:

https://github.com/alphagov/backdrop-ga-trending-collector/pull/1

https://github.com/alphagov/backdrop-pingdom-collector/pull/16

https://github.com/alphagov/backdrop-ga-realtime-collector/pull/29

https://github.com/alphagov/backdrop-ga-collector/pull/55

https://github.gds/gds/pp-deployment/pull/229