Messaging Notifications

[micahalcorn]

Browser nNotifications are currently only triggered by offer-related events. The notifications server should also be aware of messaging-related events and push these to subscribing recipients.

[micahalcorn]

The status quo:

• Here the messaging server notifies the linking server of a new message (for mobile push notifications).
• Here the notifications server listens for offer-related events (from the discovery listener).
• Here the notifications server notifies the linking server of a new offer-related event (for mobile push notifications).

Perhaps the notifications server should be responsible for all posts to the linking server regardless of source. I'm not sure whether or not the linking server correctly handles those.

cc @Natasha08 & @tomlinton (in case the are tunneling restrictions that will need to evolve)

[micahalcorn]

To Do (somewhat related): refine all of the copy for the actual message strings that are pushed.

[micahalcorn]

Bumping this up to 🅿️1️⃣ in accordance with sprint planning and shifting the scope from browser push to email.

[wanderingstan]

Gonna call this done with #2257

[micahalcorn]

Done ✅