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/en_US/Contact.json

@@ -23,6 +23,7 @@
         "cAdressenContact": "Addresses",
         "cVmhRumungsklageContact": "Eviction Lawsuits (Portal)",
         "cMietinkassoContact": "Rent Collection",
+        "cKuendigungContact": "Terminations (Portal)",
         "cBankverbindungenContact": "Bank Accounts"
     },
     "options": {