feat(ci): add config for cross-repo testing
feat(ci): add config for cross-repo testing

https://github.com/mozilla/fxa-auth-server/pull/1621

r=vladikoff
mozilla/fxa-auth-server,mozilla/fxa-auth-server,mozilla/fxa-auth-server,eoger/fxa-auth-server,eoger/fxa-auth-server,mozilla/fxa-auth-server,eoger/fxa-auth-server,eoger/fxa-auth-server