fix: add comment warning about grpc compatibility

Author: jschneidereit

jdbc-core/src/main/java/com/salesforce/datacloud/jdbc/core/DataCloudJdbcManagedChannel.java

@@ -73,7 +73,7 @@ public HyperServiceGrpc.HyperServiceBlockingStub getStub(Properties properties,
 
         if (!queryTimeout.isZero() && !queryTimeout.isNegative()) {
             log.info("Built stub with queryTimeout={}, interceptors={}", queryTimeout, interceptors.length);
-            stub = stub.withDeadlineAfter(queryTimeout.getSeconds(), TimeUnit.SECONDS);
+            stub = stub.withDeadlineAfter(queryTimeout.getSeconds(), TimeUnit.SECONDS); // COMPATIBILITY WARNING: do not use Duration overload since older versions of gRPC don't have it
         } else {
             log.info("Built stub with queryTimeout=none, interceptors={}", interceptors.length);
         }