replace `payload` with `input claim set`

I thought the intent of #274 was to introduce a proper term for what would be the raw unredacted input into the whole process before SD processing to add _sd and ... with the digest values. I think payload is fine as we use it and consistent with how JWT/JWS us the term. And don't think "input claim set" is a good or accurate replacement for payload.

i.e. we were looking to have a nice term to distinguish the "set of claims that the Issuer is issuing"

{
  "sub": "john_doe_42",
  "given_name": "John",
  "family_name": "Doe",
  "email": "johndoe@example.com",
  "phone_number": "+1-202-555-0101",
  "address": {
    "street_address": "123 Main St",
    "locality": "Anytown",
    "region": "Anystate",
    "country": "US"
  },
  "birthdate": "1940-01-01"
}

from the actual "payload of an SD-JWT"

{
  "_sd": [
    "5nXy0Z3QiEba1V1lJzeKhAOGQXFlKLIWCLlhf_O-cmo",
    "9gZhHAhV7LZnOFZq_q7Fh8rzdqrrNM-hRWsVOlW3nuw",
    "S-JPBSkvqliFv1__thuXt3IzX5B_ZXm4W2qs4BoNFrA",
    "bviw7pWAkbzI078ZNVa_eMZvk0tdPa5w2o9R3Zycjo4",
    "o-LBCDrFF6tC9ew1vAlUmw6Y30CHZF5jOUFhpx5mogI",
    "pzkHIM9sv7oZH6YKDsRqNgFGLpEKIj3c5G6UKaTsAjQ",
    "rnAzCT6DTy4TsX9QCDv2wwAE4Ze20uRigtVNQkA52X0"
  ],
  "iss": "https://example.com/issuer",
  "iat": 1516239022,
  "exp": 1735689661,
  "_sd_alg": "sha-256",
  "cnf": {
    "jwk": {
      "kty": "EC",
      "crv": "P-256",
      "x": "TCAER19Zvu3OHF4j4W4vfSVoHIP1ILilDls7vCeGemc",
      "y": "ZxjiWWbZMQGHVWKVQ4hbSIirsVfuecCE6t4jT9F2HZQ"
    }
  }
}

oauth-wg / oauth-selective-disclosure-jwt

replace `payload` with `input claim set` #306