Update TopNQuery to support multiple stages (#85)

Signed-off-by: Gao Hongtao <hanahmily@gmail.com>

Author: hanahmily

src/main/java/org/apache/skywalking/banyandb/v1/client/TopNQuery.java

@@ -34,6 +34,7 @@ public class TopNQuery {
     private final int number;
     private final AbstractQuery.Sort sort;
     private MeasureQuery.Aggregation.Type aggregationType = MeasureQuery.Aggregation.Type.UNSPECIFIED;
+    private  List<String> stages;
     /**
      * Query conditions.
      */
@@ -69,6 +70,11 @@ BanyandbMeasure.TopNRequest build() throws BanyanDBException {
                 bld.addConditions(expr.build().getCondition());
             }
         }
+        if (stages != null && !stages.isEmpty()) {
+            for (String stage : stages) {
+                bld.addStages(stage);
+            }
+        }
         return bld.build();
     }
 }