Enable Prometheus Response and System metrics for www-gitlab-com

We should look into how we can enable Prometheus monitoring of the Response and System metrics for www-gitlab-com. I tried to find where we currently collect this, but was not able to locate on performance.gitlab.net.

Steps should be:

1. Identify what Prometheus server is currently monitoring www-gitlab-com
2. Learn what service is hosting it, and if there is a load balancer in front.
3. See if we can support OOTB, or if we need to make some label detection changes.