Investigate switching Snowplow storage strategy from local storage to cookie

Problem

Currently, Snowplow uses the localStorage storage strategy. This has the unfortunate side effect is that the session_id never resets which leads to session count equaling user count. See https://discourse.snowplowanalytics.com/t/session-not-tracked-correctly/3026 and https://gitlab.com/gitlab-data/analytics/issues/2023#note_194924899

Proposal

Switch to Cookie

Result

Next steps (if any)

FYI @tipyn @donaldcook @mpeychet @eli_kastelein