fix - filter out highlight col in result schema

Signed-off-by: Jialiang Liang <jiallian@amazon.com>

Author: RyanL1997

protocol/src/main/java/org/opensearch/sql/protocol/response/QueryResult.java

@@ -74,8 +74,8 @@ public int size() {
    */
   public Map<String, String> columnNameTypes() {
     Map<String, String> colNameTypes = new LinkedHashMap<>();
-    schema
-        .getColumns()
+    schema.getColumns().stream()
+        .filter(column -> !HIGHLIGHT_FIELD.equals(getColumnName(column)))
         .forEach(
             column ->
                 colNameTypes.put(