Create VSCE campaign events on sourcegraph.com
Created by: philipp-spiess
This is a cherry-picked commit from https://github.com/sourcegraph/sourcegraph/pull/30963 to enable the tracking of the new VSCE related UTM campaigns on sourcegraph.com.
We need to land this in a separate PR as the VSCE currently lives in a diverged branch but that branch does not deploy onto sourcegraph.com.
Test plan
To validate that this logs the right parmeters I changed the hostname to my local instance: https://sourcegraph.test:3443/sign-up?editor=vscode&utm_medium=VSCIDE&utm_source=sidebar&utm_campaign=vsce-sign-up&utm_content=sign-up
and verified that the events show up in the console: