As a product manager I want telemetry in the agg pipeline builder

As a product manager I want telemetry in the agg pipeline builder so I can see how our customers use the interface. Interesting questions to ask:

• How long was spent building the pipeline?
• How many stages was the pipeline?
• What are the most frequently used stages?
• What are some common mistakes made?
• What is the size of the sample set by users?
• How often does someone get stuck writing a pipeline / fail to create a valid pipeline?