Set push notifications icon to be the app icon

[epou]

See:

• https://stackoverflow.com/a/44848340/8450576
• https://firebase.google.com/docs/cloud-messaging/android/receive
• https://stackoverflow.com/questions/37325051/notification-icon-with-the-new-firebase-cloud-messaging-system

[DigitalSeneca]

When trying on my phone, I get the app icon like in the screenshot. When I try in a dev emulator I don't get the app icon.

[aescobarr]

On a Google Pixel 6a, Android 14, the notifications look like this: