Dedicated Docs for JWT and VC JWTs

[nitro-neal]

Clarify: https://www.w3.org/TR/vc-data-model/#jwt-decoding Originally from https://github.com/TBD54566975/web5-js/pull/421/files

Clarify the language and vc jwt examples for these claims:

• If any of these steps fail, the function will throw a [Error] with a message indicating the nature of the failure:

• • exp MUST represent the expirationDate property, encoded as a UNIX timestamp (NumericDate).
• • iss MUST represent the issuer property of a verifiable credential or the holder property of a verifiable presentation.
• • nbf MUST represent issuanceDate, encoded as a UNIX timestamp (NumericDate).
• • jti MUST represent the id property of the verifiable credential or verifiable presentation.
• • sub MUST represent the id property contained in the credentialSubject.

• Once the verifications are successful, when recreating the VC data model object, this function will:

• • If exp is present, the UNIX timestamp MUST be converted to an [XMLSCHEMA11-2] date-time, and MUST be used to set the value of the expirationDate property of credentialSubject of the new JSON object.
• • If iss is present, the value MUST be used to set the issuer property of the new credential JSON object or the holder property of the new presentation JSON object.
• • If nbf is present, the UNIX timestamp MUST be converted to an [XMLSCHEMA11-2] date-time, and MUST be used to set the value of the issuanceDate property of the new JSON object.
• • If sub is present, the value MUST be used to set the value of the id property of credentialSubject of the new credential JSON object.
• • If jti is present, the value MUST be used to set the value of the id property of the new JSON object.

[KendallWeihe]

Also relevant to this https://github.com/TBD54566975/web5-spec/issues/134

@decentralgabe I think we need dedicated docs around JWT thangs, like we did for VCs and DIDs