Refactor the IDR specification - to separate registered IDs from self-issued IDs

Created by: onthebreeze

Impacted sections

https://spec-untp-fbb45f.opensource.unicc.org/docs/specification/IdentityResolver

Issue Description

In our IDR specification we present a way for all identifiers to be "D-R-V" - namely Discoverable, Resolvable, Verifiable. And we organise the document that way. But we also show how that can work for either registered identifiers managed by a scheme operator - or self-issued identifiers (DIDs). But it's a bit confusing because the current top level structure follows D-R-V with bits of DID vs rgistered scheme mixed into those headings.

Buit in reality as an implemener you are either using a registered scheme or you are self-issuing DIDs. So I suggest to re-factor the IDR page where the top level is identifiers type (registered scheme or Self-isued) and then within that we talk about how to do D-R-V in each case. Should make the whole thing a lot cleaner and easier to understand,