feature(snippet): add survey snippet for some en users

<del>Don't merge until we get approval on the strings.</del> Ready to go, pending review of latest changes by @pdehaan or equivalent LV 99 QA mage. Fixes #1206.
I think `<=` is backwards and should be `>`? `percent` is `MARKETING_PERCENTAGE`. Currently, 10% of users will have their marketing overridden, where it looks like 10% should see the marketing.