insights: pings are aggregated on incorrect user_id

Created by: coury-clark

Some of the code insights pings are aggregated on a field called anonymous_user_id instead of user_id. This impacts how things such as "first time insight creator" are calculated, because it isn't correctly grouping by users.

Some context from slack https://sourcegraph.slack.com/archives/C014ZCKMCAV/p1633590127351400?thread_ts=1633361848.291000&cid=C014ZCKMCAV