Fix .well-known URL descriptions

[tomdaffurn]

RFC8414 (OAuth 2.0 Authorization Server Metadata) defines an algorithm to transform Issuer Identifier into the well known URL. Our description of it is incomplete, particularly with respect to handling path components.

OID4VCI credential issuer metadata use a slightly different transform for URLs with path components.

Suggest we link to RFC8414 and OID4VCI specs to define the transforms, rather than reproducing it in our spec.