add support for exists query syntax in query parser (#2170)

* add support for exists query syntax in query parser

* rustfmt

* make Exists require a field

src/query/query_parser/query_parser.rs

@@ -847,6 +847,12 @@ impl QueryParser {
                 }));
                 (Some(logical_ast), errors)
             }
+            UserInputLeaf::Exists { .. } => (
+                None,
+                vec![QueryParserError::UnsupportedQuery(
+                    "Range query need to target a specific field.".to_string(),
+                )],
+            ),
         }
     }
 }