feat: support cloud event deserialization out of the box

[a-wallen]

Description

Support for context.request.pubsub() similar to context.request.json() immediately.

This may work well as a package, but to be honest, I am not sure what the best way is.

I have a few services that I've deployed to cloud run that respond to various Eventarc events.

Would be nice to have this functionality out of the box.

Requirements

• Implement context.request.pubsub()
• Implement context.request.firestoreDocument()

[jhuckabee]

I like the thinking behind this. Two questions for you @a-wallen...

1. What do you envision as the return type of the two methods listed in your requirements? Is that an object from google_cloudevents_dart? For context.request.firestoreDocument() my mind immediately goes to DocumentEventData (defined here).
2. Does this also imply that we'd have essentially a method per system? e.g. context.request.storage for a Cloud Storage events, context.request.alloydb for AlloyDB events, etc.

[a-wallen]

What do you envision as the return type of the two methods listed in your requirements? Is that an object from google_cloudevents_dart? For context.request.firestoreDocument() my mind immediately goes to DocumentEventData (defined here).

Yes, that would be the idea.

Does this also imply that we'd have essentially a method per system? e.g. context.request.storage for a Cloud Storage events, context.request.alloydb for AlloyDB events, etc.

Yes, we would support all cloud events.

This may be best suited as an extension library.