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/ios/.gitignore

@@ -0,0 +1,10 @@
+.DS_Store
+/.build
+/Packages
+/*.xcodeproj
+xcuserdata/
+DerivedData/
+.swiftpm/config/registries.json
+.swiftpm/xcode/package.xcworkspace/contents.xcworkspacedata
+.netrc
+Package.resolved