[iOS] Fix: ITMS-90078: Missing Push Notification Entitlement

[suho]

Issue

Currently, when deploying an iOS build to TestFlight from the flutter templates, we will have this warning email from Apple:

It's better to fix the project and not to receive the warning email above.

Expected

No warning emails from Apple after deploying iOS builds to TestFlight.

Steps to reproduce

1. Create a new project from flutter templates.
2. Deploy an iOS build to TestFlight.
3. Then check the email box to see the warning email.