Track events from onboarding emails

Created by: rrhyne

We currently do not track inbound events generated from our onboarding mechanisms.

This means we are unable to determine the effectiveness of our email programs at creating engagement, improving retention and completing important actions such as adding code hosts and sync repositories.

Onboarding emails contain UTM parameters that describe the campaign. We can use these parameters to generate EventLog events which can be tracked in both Amplitude and Looker.

See this thread for more details: https://sourcegraph.slack.com/archives/CN4FC7XT4/p1641475183006200

Note: we are waiting on the correct UTM parameters to trigger on.