Fixes #13266

When google_firebase_project is used, it adds a label firebase:enabled to the underlying GCP project. This label will be accidentally deleted when running terraform apply again because the label isn't present in the google_project resource block. This has caused Firebase projects created in Terraform to not show in the Firebase Console and Firebase CLI.

While we can't 100% prevent users from deleting the label, at least the examples should be correct.

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Release Note Template for Downstream PRs (will be copied)

google_project: fixes misleading examples that could cause `firebase:enabled` label to be accidentally removed.

Derived from GoogleCloudPlatform/magic-modules#7149