Code review comment for ~d0ugal/maas:release-notification-setting

I understand you're using a list so future notification types can be toggled. The Config model has API and websocket code so new values should just work. As this is a new type you may need to modify those as well. I wonder if we should keep this as a simple boolean as that is what the design calls for. In the future we could create new boolean config values as well if need be.