File integrity of documents

[jpmckinney]

Split from #1724

For hashes and digital signatures, we can consider adding to the Document subschema an integrity array, to allow for any kind of hash (sha256, etc.) This array can be composed of objects that reuse the existing Identifier subschema, where scheme can be set to "sha256", "ipfs", etc. and id can be the hash or signature. So:

{
  "tender": {
    "documents": [
      {
        "integrity": [
          {
            "scheme": "sha384",
            "id": "oqVuAfXRKap7fdgcCY5uykM6+R9GqQ8K/uxy9rx7HNQlGYl1kPzQho1wx4JwY8wC"
          }
        ]
      }
    ]
  }
}

[pdiadia]

Thank you, I agree with this proposal.