removed custom webhooks authn

[elf-pavlik]

I'm starting it as a draft since it needs some more work.

@jaxoncreed do you think we can break up this document into a spec and a primer?

• spec - would intentionally leave AuthN out of scope, only mentioning Solid-OIDC in a non-normative way.
• primer - would show all the details and use specifically Solid-OIDC to provide complete guidance.

TODO

• adjust conformance classes based on Update conformance model #120

[jaxoncreed]

Yeah I think that makes a lot of sense.

[elf-pavlik]

#146 defines WebhookChannel2023

Once we merge it we can write a primer to accompany it.