issue https://github.com/TryGhost/Team/issues/614
- The feature flag was called `oauthLogin` instead of simply `oauth` to avoid clashes in the frontend `feature` service as it is merging the config and labs properties.
- This is part of the quest to separate the frontend and server & get rid of all the places where there are cross-requires
- At the moment the settings cache is one big shared cache used by the frontend and server liberally
- This change doesn't really solve the fundamental problems, as we still depend on events, and requires from inside frontend
- However it allows us to control the misuse slightly better by getting rid of restricted requires and turning on that eslint ruleset
no issue
- moved `config` and `site` API output generation to a `public-config` service allowing all API versions to use `publicConfig.config` or `publicConfig.site` in their query methods
- updated `config` and `site` API output serializers to use an allow-list that limits the data returned for each API version
