Standardize specification links

[tomdaffurn]

We should standardize all the links to specs to a single host and version for each type.

The RFC links we are using point to several hosts:

• https://datatracker.ietf.org/
• https://www.rfc-editor.org/

OID4VCI has 2 versions

• https://openid.net/specs/openid-4-verifiable-credential-issuance-1_0.html
• https://openid.github.io/OpenID4VCI/openid-4-verifiable-credential-issuance-wg-draft.html