Properly documenting the eventual move from 5277 one way notifications to subscribed-messages

[ericvoit]

5277 provides the mechanism for one way negotiation encoding. Unfortunately, it doesn't include the ability to support some headers.

v05 of this draft proposes wording which hopefully will allow migration to the new notification-messages header without causing any revisions to this document. However IETF process might not allow such a migration without a revision to this document. This issue is to allow us to track the best way to cover the documentation so that this issue isn't lost.

(Notes from Martin on this)

Ok, I think I know what you mean; you want this spec to use 5277
for now, but when we define a new notification message, that one
should be used instead. But the current text with MAY is too lax,
imo. I think it should be a MUST, and when the new notification
message document is published, it can update this document.

Yes, this is what is intended. I was hoping to use MAY so that we
didn't have to revisit this document. I am happy to go with whatever
approach works for everyone.

[ericvoit]

Current draft removes any normative reference to the new notification-messages draft, and acknowledges that we should update this document when notification-messages completes.