Deploy to a cluster and contact us link in search performance warning notice is relative, not absolute

Created by: ryan-blunden

1. Go to https://demo.sgdev.org
2. Search for (hunk|repository)resolver index:only timeout:1000s
3. Notice Search performance warning shown. Click on Contact us link.
4. Taken to repo 404 page as the link was /https://about.sourcegraph.com/contact.