REST API: Skip setting up push notification if authenticated without WPCom

[itsmeichigo]

Part of #8453

Description

This PR updates the push notification setup logic by skipping the setup if the user is authenticated without WPCom.

Testing instructions

• Delete the app on your physical device if it's already installed.
• Turn on the feature flag applicationPasswordAuthenticationForSiteCredentialLogin and build the app to the device.
• Log out of the app or skip onboarding if needed.
• On the prologue screen, select Enter your site address and proceed with the address of your self-hosted site.
• Log in with your site credentials.
• After the login succeeds, you should be navigated to the home screen. There should be no alert for push notification permission. Neither of the methods didRegisterForRemoteNotificationsWithDeviceToken and didFailToRegisterForRemoteNotificationsWithError on AppDelegate should be triggered.

Screenshots

N/A

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• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[wpmobilebot]

You can test the changes from this Pull Request by:

• Clicking here or scanning the QR code below to access App Center
• Then installing the build number pr8665-07101d8 on your iPhone

If you need access to App Center, please ask a maintainer to add you.

[selanthiraiyan]

This works as expected. 🚢