log active external extensions from Sourcegraph.com
Created by: vanesa
Log active external extensions from Sourcegraph.com, update changelog and the pings documentation (https://docs.sourcegraph.com/admin/pings).
Test plan:
run localStorage.eventLogDebug="true";
in the browser console and select log levels to be Verbose
. Go to any Sourcegraph page on your localhost instance and see the EVENT <name of active extension>
showing the external (non-language) extensions that are currently active.