Check if it is possible to add "first sourcegraph url" property for browser extension event logs (similar to web event logs)

Created by: erzhtor

Browser extension event logs currently don't send "first sourcegraph URL". It is stored in cookies when sent to Sourcegraph GraphQL API. Check if it is possible somehow retrieve it from the background script (see chrome extension API for reading cookies, or also maybe backend implementation to get from cookies directly. If yes, then we need to implement it.

See slack discussion