Make Data Stream Notifications a sub-tab of Notifications (and depend on farm_notification).

modules/core/data_stream/modules/notification/data_stream_notification.info.yml

@@ -5,3 +5,4 @@ package: farmOS
 core_version_requirement: ^9
 dependencies:
   - farm:data_stream
+  - farm:farm_notification

modules/core/data_stream/modules/notification/data_stream_notification.links.task.yml

@@ -1,5 +1,5 @@
 data_stream_notification.settings:
-  base_route: farm_settings.settings_page
   route_name: entity.data_stream_notification.collection
-  title: 'Data Stream Notifications'
+  parent_id: farm_notification.settings
+  title: 'Data Streams'
   weight: 10

modules/core/data_stream/modules/notification/data_stream_notification.post_update.php

@@ -0,0 +1,15 @@
+<?php
+
+/**
+ * @file
+ * Post update functions for Data Stream Notifications module.
+ */
+
+/**
+ * Install farmOS Notifications module.
+ */
+function data_stream_notification_post_update_enable_farm_notification(&$sandbox = NULL) {
+  if (!\Drupal::service('module_handler')->moduleExists('farm_notification')) {
+    \Drupal::service('module_installer')->install(['farm_notification']);
+  }
+}