app.cloud.gov domains do not allow fec.gov image resources

[patphongs]

Summary

Content security policy is not allow images from fec.gov domain on any of our app.cloud.gov environments. This is most prevalent in fec-prod-proxy.app.cloud.gov domains when trying to pull in image resources from fec.gov

How to Reproduce

• Image here appears to be broken on prod app.cloud.gov environment: https://fec-prod-proxy.app.cloud.gov/updates/early-bird-discount-san-diego-conference-expires-9-27-19/
• The image on fec.gov is ok, because it allows self. https://www.fec.gov/updates/early-bird-discount-san-diego-conference-expires-9-27-19/

Completion Criteria

• Images preview correctly when users are drafting pages in wagtail and other apps.