fix(config): set localhost default value for REANA_HOSTNAME (#717)

This PR is part of harmonizing the treatment of REANA_HOSTNAME
accross all REANA components. You can refer to other PRs below.

reanahub/reana#867
reanahub/reana-workflow-controller#630

Closes reanahub/reana#865

reana_server/config.py

@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 #
 # This file is part of REANA.
-# Copyright (C) 2017, 2018, 2019, 2020, 2021, 2022, 2023, 2024 CERN.
+# Copyright (C) 2017, 2018, 2019, 2020, 2021, 2022, 2023, 2024, 2025 CERN.
 #
 # REANA is free software; you can redistribute it and/or modify it
 # under the terms of the MIT License; see LICENSE file for more details.
@@ -32,7 +32,7 @@
 
 SHARED_VOLUME_PATH = os.getenv("SHARED_VOLUME_PATH", "/var/reana")
 
-REANA_HOSTNAME = os.getenv("REANA_HOSTNAME")
+REANA_HOSTNAME = os.getenv("REANA_HOSTNAME", "localhost")
 
 REANA_SSO_CERN_CONSUMER_KEY = os.getenv("CERN_CONSUMER_KEY", "CHANGE_ME")
 REANA_SSO_CERN_CONSUMER_SECRET = os.getenv("CERN_CONSUMER_SECRET", "CHANGE_ME")

reana_server/utils.py

@@ -537,7 +537,7 @@ def __len__(self):
 
 
 def get_workspace_retention_rules(
-    retention_days: Optional[Dict[str, int]]
+    retention_days: Optional[Dict[str, int]],
 ) -> List[Dict[str, any]]:
     """Validate and return a list of retention rules.