Report additional fields in validation stream:

The HardenedValidations amendment introduces additional fields
in validations:

- `sfValidatedHash`, if present, is the hash the of last ledger that
  the validator considers to be fully validated.
- `sfCookie`, if present, is a 64-bit cookie (the default
  implementation selects it randomly at startup but other
  implementations are possible), which can be used to improve the
  detection and classification of duplicate validations.
- `sfServerVersion`, if present, reports the version of the software
  that the validator is running. By surfacing this information,
  server operators gain additional insight about variety of software
  on the network.

If merged, this commit fixes #3797 by adding the fields to the
`validations` stream as shown below:

- `sfValidateHash` as `validated_hash`: a 256-bit hex string;
- `sfCookie` as `cookie`: a 64-bit integer as a string; and
- `sfServerVersion` as `server_version`: a 64-bit integer as
  a string.

src/ripple/app/misc/NetworkOPs.cpp

@@ -2009,6 +2009,15 @@ NetworkOPsImp::pubValidation(std::shared_ptr<STValidation> const& val)
         jvObj[jss::signing_time] = *(*val)[~sfSigningTime];
         jvObj[jss::data] = strHex(val->getSerializer().slice());
 
+        if (auto version = (*val)[~sfServerVersion])
+            jvObj[jss::server_version] = std::to_string(*version);
+
+        if (auto cookie = (*val)[~sfCookie])
+            jvObj[jss::cookie] = std::to_string(*cookie);
+
+        if (auto hash = (*val)[~sfValidatedHash])
+            jvObj[jss::validated_hash] = strHex(*hash);
+
         auto const masterKey =
             app_.validatorManifests().getMasterKey(signerPublic);