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/scopes/CKuendigung.json

@@ -0,0 +1,11 @@
+{
+    "entity": true,
+    "layouts": true,
+    "tab": true,
+    "acl": true,
+    "customizable": true,
+    "type": "BasePlus",
+    "module": "Custom",
+    "object": true,
+    "isCustom": true
+}