feat(config): allow customisation of runtime group name (reanahub#440)

Closes reanahub/reana-workflow-controller#561

reana_commons/config.py

@@ -303,11 +303,18 @@ def kubernetes_node_label_to_dict(node_label):
 WORKFLOW_RUNTIME_USER_NAME = os.getenv("WORKFLOW_RUNTIME_USER_NAME", "reana")
 """Default OS user name for running job controller."""
 
+WORKFLOW_RUNTIME_GROUP_NAME = os.getenv("WORKFLOW_RUNTIME_GROUP_NAME", "root")
+"""Default OS group name for running job controller."""
+
 WORKFLOW_RUNTIME_USER_UID = os.getenv("WORKFLOW_RUNTIME_USER_UID", 1000)
 """Default user id for running job controller/workflow engine apps & jobs."""
 
 WORKFLOW_RUNTIME_USER_GID = os.getenv("WORKFLOW_RUNTIME_USER_GID", 0)
-"""Default group id for running job controller/workflow engine apps & jobs."""
+"""Default group id for running job controller/workflow engine apps & jobs.
+
+If the group id is changed to a value different than zero, then also the
+`WORKFLOW_RUNTIME_GROUP_NAME` needs to be changed to a value different than `root`.
+"""
 
 REANA_USER_SECRET_MOUNT_PATH = os.getenv(
     "REANA_USER_SECRET_MOUNT_PATH", "/etc/reana/secrets"