Update DataIntegrityProof proofValue admissible encodings

[Wind4Greg]

In Section 2.2.1 DataIntegrityProof the proof value is required to be "encoded using the base-58-btc header and alphabet", however for ECDSA-SD variants 3.4.2 serializeBaseProofValue and 3.4.7 serializeDerivedProofValue we require:

• "baseProof to a string with the Multibase base64url-no-pad-encoding of proofValue..."
• "derived proof as a string with the base64url-no-pad-encoding of proofValue..."

Hence it seems that section 2.2.1 needs to be updated to permit the base64url-no-pad-encoding as well as the base-58-btc.

[Wind4Greg]

This has been fixed, though I'm not sure which PR did it. See current draft: https://w3c.github.io/vc-di-ecdsa/#dataintegrityproof, i.e.,

"The value of the proofValue property is produced according to the cryptosuite type and is specified in either Section 3.2.1 Create Proof (ecdsa-rdfc-2019), or Section 3.3.1 Create Proof (ecdsa-jcs-2019), or Section 3.6.1 Create Base Proof (ecdsa-sd-2023), or Section 3.6.6 Add Derived Proof (ecdsa-sd-2023)."

And each of these subsections specify the encodings.