Add PQC support for the auth proofs

v1 of did:webvh requires that auth and witness proofs use eddsa keys. For the next version, suggest that we allow the use of both eddsa keys and PQC ML-DSA 44 keys. The use of multikey, did:key will ensure that a verifier can determine the type of key being used (plus, there is the size of the key...). As well, the use of Data Integrity proofs mean the code changes are minimal -- once the DI Proof cryptosuite for ML-DSA is official.

From my understanding, NIST considers ML-DSA 44 to be the PQC "replacement" for EDDSA use cases.

Experiments have been run using ML-DSA 44 keys with did:webvh, and the high level overview is that the file size is about 10x over EDDSA, and the processing time is about 10x slower vs. EDDSA. Not bad!

We will have to make sure that we can find production ready implementations of ML-DSA 44. The ones identified so far have "not for production" warnings.