Remove duplicate Workhorse logging code

This MR removes Workhorse code duplication between internal/log and internal/helper. The helper.CaptureAndFail method, and friends such as helper.Fail500, use logging helpers that duplicate code in internal/log. The natural solution would be to have internal/helper depend on internal/log. But that is impossible because internal/log already depends on internal/helper for submitting errors to Sentry.

By moving the Sentry related code into a new package internal/helper/exception we can resolve the import cycle and remove the duplicated logging code from internal/helper.