Proxy for handling Snowplow events

Overview

In https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/6642, we merged a Snowplow integration that allowed us to track events on GitLab.com. Our current implementation does not go very far - it provides basic tracking for pageviews and pagepings, and we'd like to track page interactions as well.

Before we can go further, we need to set up a system for pseudonymizing any sensitive information we may track in the future before we send any information to our collection endpoint. Security and privacy are paramount concerns, and we only are interested in tracking users across pages/activities for the purposes of improving the product.

In order to accomplish this, it might make sense to send events through an endpoint that hashes any attributes we consider PII before sending them on to the Snowplow collector.