Fix docs value for service account examples, change notebooks instanc…

[modular-magician]

…e_owners

The GOOGLE_SERVICE_ACCOUNT environment variable is just an email, but our example in documentation included an emailAddress: prefix. Fix that.

Additionally, the instance_owners value in the notebooks full example appeared to correspond to a GCP account, not an outside one. For simplicity, just use the same SA- the owner needs permission to act as the notebooks SA.

Fixes #14082

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Derived from GoogleCloudPlatform/magic-modules#7530

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