Add Google Tag snippet
Created by: aileenrose
My first PR here. Please confirm this change is for sourcegraph.com only.
This is just the Google Tag snippet only. The goal is to add GA tracking to all sourcegraph.com pages. Initially, I will only configure tracking for just the sign-up page. This is all managed via the Google Tag Manager admin.
With this PR, will there be a staging site that I could use for testing?