SIENTIAPDE-1645: Rename Prometheus 'sientia_app_up' metric to 'app_up' and update test assertion.

tests/test_metrics.py

@@ -10,7 +10,7 @@ def test_app_up_metric_exists():
     from model_manager.metrics import APP_UP
 
     assert APP_UP is not None
-    assert APP_UP._name == 'sientia_app_up'
+    assert APP_UP._name == 'app_up'
     assert (
         APP_UP._documentation == 'Indicates if the application is running (1) or shutting down (0)'
     )