Please read this: Firebase Cloud Messaging (FCM) is the new version of GCM. So, the important info is that - yes, we should prefer Firebase Console instead of Google Cloud Console. This is also a useful article: Enabling Google Cloud Messaging (Firebase).
So, you need to enable Google Cloud Messaging in Firebase Console for your added Android App.
Let me write it down for you stepwise:
1. Open your Firebase Console
2. Add your Android app in Firebase Console
3. Go to Settings
4. Click on CLOUD MESSAGING tab
5. Take Legacy Server key and use it in Azure Push Notification Service for Google(GCM) settings
6. Save it
This article will help you in creating a Notification Hub Service in Azure and connecting your Android or IOS App to Firebase Console etc.
Hope this helps :)