Include user on snowplow events

Summary

With #321329 (closed) we gave the possibility to add project, user and namespace to Snowplow events. We're not emitting this data yet. As we're moving forward with de-identification in &6309 (closed) and declared what data will be de-identified we want to move forward and collect user ID it when we have green light from product.

Potential solution

1. Add user_id to our standard context
2. Roll it out behind a feature flag, so we can turn it on once approved
3. Use an actor-based feature flag so we can roll it out to PI users first for testing

Dependency

• Adding user: We can only roll this out once we have communicated this & deployed the de-identification service