feat: saveToken plugin for app groups on iOS

This will allow the share extension to access the Bearer token to send
images to the backend.

tauri-plugin-ios-shared-token/guest-js/index.ts

@@ -0,0 +1,12 @@
+import { invoke } from "@tauri-apps/api/core";
+
+export async function saveToken(token: string) {
+    return await invoke<{ token?: string }>(
+        "plugin:ios-shared-token|saveToken",
+        {
+            payload: {
+                token,
+            },
+        },
+    );
+}