Add notification messages for office filling in German and English locales

- Added new notification messages for when a political office is filled in both the German and English locale files.
- Ensured consistency in messaging across different languages to enhance user experience.

frontend/src/i18n/locales/en/falukant.json

@@ -18,6 +18,7 @@
         },
         "notifications": {
             "notify_election_created": "A new election has been scheduled.",
+            "notify_office_filled": "A political office has been filled.",
             "production": {
                 "overproduction": "Overproduction: your production is {value} units above demand{branch_info}."
             },