refactor: decrease max_page_size to 500

- Fetching the heaviest endpoint (TH2) using page_size=1000 took almost
  20 seconds and returned 149M (tracker - StreamExpress 2024A - 378294 -
PixelPhase1/Tracks/PXForward/clusterposition_xy_ontrack_PXDisk_-1). To
avoid reaching the 30 seconds limit, page_size=500 is doable for the
same parameters (76.6M, 13 seconds).

backend/utils/pagination.py

@@ -19,7 +19,7 @@ class DynamicMultiOrderingCursorPagination(CursorPagination):
     cursor_query_param = "next_token"
     ordering_param = "order_by"
     page_size_query_param = "page_size"
-    max_page_size = 1000
+    max_page_size = 500
 
     def get_ordering(self, request, queryset, view):
         default_order_by = list(queryset.query.order_by)

frontend/src/views/browser/index.jsx

@@ -13,7 +13,7 @@ import API from '../../services/api'
 import { buildTree } from '../../utils/ops'
 
 const Browser = () => {
-  const defaultPageSize = 1000
+  const defaultPageSize = 500
 
   const [isLoadingDatasets, setIsLoadingDatasets] = useState(true)
   const [datasets, setDatasets] = useState()