fix: customize column description limit size in db_engine_spec (#34808)

(cherry picked from commit 75af53dc3d)

tests/integration_tests/datasource_tests.py

@@ -644,7 +644,14 @@ def test_get_samples_with_filters(test_client, login_as_admin, virtual_dataset):
         },
     )
     assert rv.status_code == 200
-    assert rv.json["result"]["colnames"] == []
+    assert rv.json["result"]["colnames"] == [
+        "col1",
+        "col2",
+        "col3",
+        "col4",
+        "col5",
+        "col6",
+    ]
     assert rv.json["result"]["rowcount"] == 0