chore: Add getPageSize() to QueryPaginator (#1987)

* add getPageSize() to QueryPaginator

* fix build

* fix lint

* add javadoc

Author: ron-gal

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/models/Query.java

@@ -407,6 +407,12 @@ public boolean advance(@Nonnull ByteString lastSeenRowKey) {
       query.builder.setRows(remaining);
       return true;
     }
+
+    /** Get the page size of the current Pagniator. For internal use only. */
+    @InternalApi
+    public int getPageSize() {
+      return this.pageSize;
+    }
   }
 
   @Override