(improvement)(Headless) The corrector adds group by field, but does not add agg field, resulting in SQL syntax errors (#1082)

Co-authored-by: jolunoluo

headless/api/src/main/java/com/tencent/supersonic/headless/api/pojo/SemanticSchema.java

@@ -96,6 +96,11 @@ public class SemanticSchema implements Serializable {
         return getElementsByDataSetId(dataSetId, metrics);
     }
 
+    public List<String> getMetricNames() {
+        return getMetrics().stream()
+                .map(SchemaElement::getName).collect(Collectors.toList());
+    }
+
     public List<SchemaElement> getEntities() {
         List<SchemaElement> entities = new ArrayList<>();
         dataSetSchemaList.stream().forEach(d -> entities.add(d.getEntity()));