Send GitLab instance and user IDs to Snowplow
See https://gitlab.com/gitlab-org/gitlab/-/issues/416621 and #192 (closed)
Follow up to !282 (merged)
For tracking unique user and instance counts, we want to send these data to Snowplow. Instance and user IDs are anonymized and sent through HTTP header fields from gitlab-rails (both SaaS and self-managed).
Edited by Matthias Käppler