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/i18n/de_DE/Contact.json

@@ -14,6 +14,8 @@
     "cMietobjekteContactPortal": "Mietobjekte (Portal)",
     "cAdressenContact": "Adressen",
     "cVmhRumungsklageContact": "Räumungsklagen (Portal)",
+    "cMietinkassoContact": "Mietinkasso (Portal)",
+    "cKuendigungContact": "Kündigungen (Portal)",
     "cBankverbindungenContact": "Bankverbindungen"
   },
   "links": {
@@ -29,6 +31,7 @@
     "cAdressenContact": "Adressen",
     "cVmhRumungsklageContact": "Räumungsklagen (Portal)",
     "cMietinkassoContact": "Mietinkasso",
+    "cKuendigungContact": "Kündigungen (Portal)",
     "cBankverbindungenContact": "Bankverbindungen"
   },
   "options": {