Return public key in the format of DID verification method

Current implementation returns the JSON as is in the Vault. Transform the response to look like DID verification method.

https://www.w3.org/TR/did-core/#example-various-verification-method-types

Example response:

{
    "id": "key1",
    "type": "JsonWebKey2020", 
    "publicKeyJwk": {
      "crv": "Ed25519", 
      "x": "VCpo2LMLhn6iWku8MKvSLg2ZAoC-nlOyPVQaO3FxVeQ", 
      "kty": "OKP", 
      "kid": "_Qq0UL2Fq651Q0Fjd6TvnYE-faHiOpRlPVQcY_-tA4A" 
    }
}