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/CMietobjekt.json

@@ -20,6 +20,7 @@
         "contact2mietobjekt": "Contacts",
         "vmhRumungsklages": "Eviction Lawsuits",
         "mietinkassos": "Rent Collection",
+        "kuendigungen": "Terminations",
         "contactsMietobjekt": "Portal Users",
         "dokumentesMietobjekt": "Documents"
     },