Simplify and fix upgrade function

Author: kamil-certat

intelmq/lib/upgrades.py

@@ -980,15 +980,22 @@ def v341_new_fields(configuration, harmonization, dry_run, **kwargs):
     """
     Add new fields to IntelMQ Data Format
     """
-    changed = False
-    if "event" in harmonization and "severity" not in harmonization["event"]:
-        harmonization["event"]["severity"] = {
-            "description": "Severity of the event, based on the information from the source, and eventually modified by IntelMQ during processing. Meaning of the levels may differ based on the event source.",
-            "length": 10,
-            "regex": "^(critical|high|medium|low|info|undefined)$",
-            "type": "LowercaseString",
-        }
-        changed = True
+    changed = None
+    if "event" not in harmonization:
+        return changed, configuration, harmonization
+
+    builtin_harmonisation = load_configuration(
+        resource_filename("intelmq", "etc/harmonization.conf")
+    )
+    for field in [
+        "severity",
+    ]:
+        if field not in harmonization["event"]:
+            if field not in builtin_harmonisation["event"]:
+                # ensure forward-compatibility if we ever remove something from harmonisation
+                continue
+            harmonization["event"][field] = builtin_harmonisation["event"][field]
+            changed = True
     return changed, configuration, harmonization