implement deletion of admin user, frontend and backend

src/routes/(angemeldet)/user-management/+page.svelte

@@ -65,8 +65,21 @@
         }, 5000);
     }
 
-    async function deleteUser() {
+    async function deleteUser(userId: number) {
+        const URL = `/api/users/${userId}`;
 
+        const response = await fetch(URL, {
+            method: 'DELETE',
+            headers: {
+                'Content-Type': 'application/json'
+            }
+        })
+
+        if (response.status == 204) {
+            userList = await getUsers();
+        } else {
+            alert("Nutzer konnte nicht gelöscht werden")
+        }
     }
 
 </script>