fix: add allowClawback flag for account_info (#4590)

* Update the `account_info` API so that the `allowClawback` flag is
  included in the response.
  * The proposed `Clawback` amendement added an `allowClawback` flag in
    the `AccountRoot` object.
  * In the API response, under `account_flags`, there is now an
    `allowClawback` field with a boolean (`true` or `false`) value.
  * For reference, the XLS-39 Clawback implementation can be found in
    #4553

Fix #4588

src/ripple/rpc/handlers/AccountInfo.cpp

@@ -96,6 +96,9 @@ doAccountInfo(RPC::JsonContext& context)
                  {"disallowIncomingPayChan", lsfDisallowIncomingPayChan},
                  {"disallowIncomingTrustline", lsfDisallowIncomingTrustline}}};
 
+    static constexpr std::pair<std::string_view, LedgerSpecificFlags>
+        allowClawbackFlag{"allowClawback", lsfAllowClawback};
+
     auto const sleAccepted = ledger->read(keylet::account(accountID));
     if (sleAccepted)
     {
@@ -123,6 +126,11 @@ doAccountInfo(RPC::JsonContext& context)
             for (auto const& lsf : disallowIncomingFlags)
                 acctFlags[lsf.first.data()] = sleAccepted->isFlag(lsf.second);
         }
+
+        if (ledger->rules().enabled(featureClawback))
+            acctFlags[allowClawbackFlag.first.data()] =
+                sleAccepted->isFlag(allowClawbackFlag.second);
+
         result[jss::account_flags] = std::move(acctFlags);
 
         // The document states that signer_lists is a bool, however