Align event subscription/notification to Commonalities r3.2

[benhepworth]

Summary

The API uses implicit notifications, but the sink, sinkCredential, and subscription definitions are not aligned with the CAMARA Event Subscription and Notification Guide for Commonalities r3.2.

Changes Required

• Align sink and sinkCredential definitions to the Event Guide
• Add sink pattern and 400 - INVALID_SINK error response
• Update types property of SubscriptionRequest to allow more than one event type per subscription
• Update types property of SubscriptionRequest to use SubscriptionEventType schema (enum of defined types)
• Rename event: subscription-ends → subscription-ended
• (Optional) Add subscription-started event
• (Optional) Add subscription-updated event

References

• Raised during review of PR r1.1 M3 release #55
• CAMARA Event Subscription and Notification Guide (r3.2): https://github.com/camaraproject/Commonalities/blob/r3.2/documentation/CAMARA-API-Event-Subscription-and-Notification-Guide.md
• Commonalities r3.2 alignment wiki: https://lf-camaraproject.atlassian.net/wiki/spaces/CAM/pages/132218881/Analysis+of+Commonalities+0.6.0-rc.1+changes

[mohdfarhanakram]

Hi @benhepworth, I would like to pick this one up as well - continuing through the batch. I have already submitted PRs for #67, #68, and #69.