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/CDokumente.json

@@ -7,6 +7,7 @@
         "vmhMietverhltnisesDokumente": "Tenancies",
         "vmhErstgespraechsdokumente": "Initial Consultations",
         "vmhRumungsklagesdokumente": "Eviction Lawsuits",
+        "kuendigungDokumente": "Terminations",
         "md5sum": "MD5 Checksum",
         "sha256": "SHA256 Checksum",
         "beteiligte2dokumente": "Parties",
@@ -17,6 +18,7 @@
         "vmhMietverhltnisesDokumente": "Tenancies",
         "vmhErstgespraechsdokumente": "Initial Consultations",
         "vmhRumungsklagesdokumente": "Eviction Lawsuits",
+        "kuendigungDokumente": "Terminations",
         "beteiligte2dokumente": "Parties",
         "mietobjekt2dokumente": "Properties",
         "mietinkassosdokumente": "Rent Collection"