Webhook subscription management API

[sdatspun2]

Webhooks are used widely by HTTP API developers, however, there is no consistent way to do the following. Some API developers are good at the following others leave it to API consumers to figure this out from documentation.

1. Get a list of events available that are delivered via webhook
2. Retrieve schema for each type of event (if applicable)
3. Subscribe to one or more event (callback url, message integrity (jws, http message signature, etc.), auth (oauth2, 2way tls, etc.)
4. Unsubscribe for one or more event
5. Retrieve the schema of a webhook so incoming webhooks can be validated and parsed correctly
6. etc.

Does this fall into this working group's scope? OpenAPI has callback object https://spec.openapis.org/oas/v3.1.0#callback-object but it is defined relative to each endpoint in the API contract. An API developer may have many such contracts. I haven't used the callback object much but perhaps someone from the WG (@darrelmiller?) can shed some light here if that callback object satisfies the requirements.