Implement politics overview feature in FalukantService and update UI

- Added a new method `getPoliticsOverview` in FalukantService to retrieve currently held offices, including office holders and term end dates.
- Enhanced the PoliticsView component to display the term end dates for current offices.
- Updated localization files to include a new message for applying to selected positions.
- Improved the handling of already applied positions in the open politics section, pre-selecting checkboxes accordingly.

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

@@ -640,7 +640,8 @@
                 "region": "Region",
                 "date": "Datum",
                 "candidacy": "Kandidatur",
-                "none": "Keine offenen Positionen."
+                "none": "Keine offenen Positionen.",
+                "apply": "Für ausgewählte Positionen kandidieren"
             },
             "upcoming": {
                 "office": "Amt",