Add documentation "How to track an event" to Frontend documentation
Based on the implementation in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/7403 and https://gitlab.com/gitlab-org/gitlab-ee/issues/7827, we need to add a section about how we can track events on the Frontend.
Topics that should be covered:
- Necessary
data-track-*
attributes (see implementation in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/7403) - How to use tracking helpers for applying tracking attributes conditionally in HAML files https://gitlab.com/gitlab-org/gitlab-ee/issues/7827
- Attaching event handlers in
stats.js
- Reference to the snowplow documentation