Instrument banner clicks on event data collection banner

In this MR we introduced a banner to inform customers about event level data collection and the option to opt-out. Use the internal events instrumentation documentation (https://docs.gitlab.com/development/internal_analytics/internal_event_instrumentation/) to help instrument an event that records clicks that close the banner.

In case the banner already has tracking, create a new section with documentation on the banner here and highlight what is tracked.