perf: change secret timedelta

apps/assets/models/automations/change_secret.py

@@ -65,3 +65,9 @@ class ChangeSecretRecord(JMSBaseModel):
 
     def __str__(self):
         return self.account.__str__()
+
+    @property
+    def timedelta(self):
+        if self.date_started and self.date_finished:
+            return self.date_finished - self.date_started
+        return None

apps/assets/serializers/automations/change_secret.py

@@ -93,8 +93,8 @@ class ChangeSecretRecordSerializer(serializers.ModelSerializer):
     class Meta:
         model = ChangeSecretRecord
         fields = [
-            'id', 'asset', 'account', 'date_started',
-            'date_finished', 'is_success', 'error', 'execution',
+            'id', 'asset', 'account', 'date_started', 'date_finished',
+            'timedelta', 'is_success', 'error', 'execution',
         ]
         read_only_fields = fields