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/Contact.json

@@ -94,6 +94,14 @@
             "audited": false,
             "isCustom": true
         },
+        "cKuendigungContact": {
+            "type": "hasMany",
+            "relationName": "cKuendigungContact",
+            "foreign": "contactsKuendigung",
+            "entity": "CKuendigung",
+            "audited": false,
+            "isCustom": true
+        },
         "cBankverbindungenContact": {
             "type": "hasMany",
             "relationName": "cBankverbindungContact",