Restore the "alternate file domain" setup warning and provide CDN instructions
Summary:
Fixes T2380. Fixes T2382. Users should really configure this, but when we had a warning before a lot of users had trouble with it.
- Tout performance benefits.
- Document easy setup via CDN.
- We have an "Ignore" button now for users who really don't care.
Test Plan:
- Set up admin.phacility.com through AWS CloudFront (need a few changes to handle instances to put it on the cluster in general).
- Set up secure.phabricator.com through CloudFlare (almost; waiting for DNS).
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: chad, epriestley
Maniphest Tasks: T2382, T2380
Differential Revision: https://secure.phabricator.com/D11649