Users may want to require authorization from a producing client that is emitting into their Event Gateway. This is particularly necessary for asynchronous subscriptions, as the subscribed consumers are decoupled from the producer and thus cannot make demands on the authorization necessary.

For this issue, we'll allow users to set authorization mechanisms on Event Types. When a producing client emits an Event, it will first check to see if the emitted Event has the needed authorization. If yes, it will continue and the producing client will receive a 202 Accepted. If not, the producing client will receive a 401 Unauthorized.

As a part of this issue following PR were created:

• Refactored Subscription model #429
• Remove invoke functionality #432
• Event types #433
• Events API Authorization (Event Type Authorizer) #441
• Add endpoint for updating event type #455
• Include authorization in the event #456
• Switch to AtomicPut in Create methods #457
• CORS Config API #460