SIENTIAPDE-1174

Refactor unit tests to improve readability and maintainability

- Updated test assertions and mock setups in test_app.py for clarity.
- Added 'pod_id' to the metadata in test_ingestor.py for consistency.
- Introduced a new test for TAG_WRITTEN_COUNT in test_metrics.py to verify its definition.
- Enhanced test data structure in test_data_manager.py to include additional fields.

tests/unit/test_ingestor.py

@@ -51,6 +51,7 @@ def test___init__(notification_handler, getenv):
         "model_name": "-",
         "workflow_name": "OPC_INGESTOR",
         "schema_name": "OPC_INGESTOR",
+        "pod_id": "localhost1"
     }
 
     notification_handler.assert_called_once_with(