feat: Add termination functionality for rental agreements

- Introduced new entity `CKuendigung` for managing terminations.
- Added fields for termination details including date, reason, type, and status.
- Implemented backend service to initiate terminations from rental agreements.
- Created frontend handler for termination actions with confirmation dialog.
- Updated metadata and layouts for `CKuendigung` to support new functionality.
- Added internationalization support for English and German languages.
- Enhanced existing entities to establish relationships with terminations.

custom/Espo/Custom/Resources/metadata/entityDefs/CBeteiligte.json

@@ -294,6 +294,22 @@
             "audited": false,
             "isCustom": true
         },
+        "kuendigungenVermieter": {
+            "type": "hasMany",
+            "relationName": "cBeteiligteKuendigungVermieter",
+            "foreign": "vermieter",
+            "entity": "CKuendigung",
+            "audited": false,
+            "isCustom": true
+        },
+        "kuendigungenMieter": {
+            "type": "hasMany",
+            "relationName": "cBeteiligteKuendigungMieter",
+            "foreign": "mieter",
+            "entity": "CKuendigung",
+            "audited": false,
+            "isCustom": true
+        },
         "dokumentesBeteiligte": {
             "type": "hasMany",
             "relationName": "cBeteiligteDokumente",