fix(useStripeProvider): safari did not route to stripe customer portal

`window.open()` does not work on `safari based browsers`

Author: marcel-bitfly

frontend/.vscode/settings.json

@@ -78,6 +78,7 @@
         "useFeatureFlag",
         "useNotificationsOverviewStore",
         "useSettingsStore",
+        "useStripeProvider",
         "useWindowSize",
         "variables.scss",
         "vscode"

frontend/composables/useStripeProvider.ts

@@ -59,7 +59,7 @@ export function useStripeProvider() {
       },
     )
 
-    window.open(res?.url, '_blank')
+    await navigateTo(res?.url, { external: true })
 
     isStripeProcessing.value = false
   }