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/clientDefs/CKuendigung.json

@@ -0,0 +1,55 @@
+{
+    "controller": "controllers/record",
+    "boolFilterList": [
+        "onlyMy"
+    ],
+    "iconClass": "fas fa-file-contract",
+    "sidePanels": {
+        "detail": [
+            {
+                "name": "activities",
+                "reference": "activities"
+            },
+            {
+                "name": "history",
+                "reference": "history"
+            },
+            {
+                "name": "tasks",
+                "reference": "tasks"
+            }
+        ]
+    },
+    "bottomPanels": {
+        "detail": [
+            {
+                "name": "activities",
+                "reference": "activities",
+                "disabled": true
+            },
+            {
+                "name": "history",
+                "reference": "history",
+                "disabled": true
+            }
+        ]
+    },
+    "relationshipPanels": {
+        "vermieter": {
+            "layout": null,
+            "selectPrimaryFilterName": null
+        },
+        "mieter": {
+            "layout": null,
+            "selectPrimaryFilterName": null
+        },
+        "dokumenteKuendigung": {
+            "layout": null,
+            "selectPrimaryFilterName": null
+        },
+        "contactsKuendigung": {
+            "layout": null,
+            "selectPrimaryFilterName": "portalUsers"
+        }
+    }
+}