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

[rileykarson]

…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 hashicorp/terraform-provider-google#14082

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• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Generated Terraform providers, and ran make test and make lint in the generated providers to ensure it passes unit and linter tests.
• Ran relevant acceptance tests using my own Google Cloud project and credentials (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 7 files changed, 10 insertions(+), 10 deletions(-))
Terraform Beta: Diff ( 7 files changed, 10 insertions(+), 10 deletions(-))
TF Validator: Diff ( 2 files changed, 3 insertions(+), 3 deletions(-))

[modular-magician]

Tests analytics

Total tests: 2523
Passed tests 2255
Skipped tests: 264
Affected tests: 4

Action taken

Found 4 affected test(s) by replaying old test recordings. Starting RECORDING based on the most recent commit. Click here to see the affected tests

TestAccNetworkServicesGateway_update|TestAccNotebooksInstance_notebookInstanceFullExample|TestAccDataSourceDnsManagedZone_basic|TestAccDataSourceGoogleCloudAssetResourcesSearchAll_basic

Get to know how VCR tests work

[modular-magician]

Tests passed during RECORDING mode:
TestAccNetworkServicesGateway_update[Debug log]
TestAccNotebooksInstance_notebookInstanceFullExample[Debug log]

Tests failed during RECORDING mode:
TestAccDataSourceDnsManagedZone_basic[Error message] [Debug log]
TestAccDataSourceGoogleCloudAssetResourcesSearchAll_basic[Error message] [Debug log]

Please fix these to complete your PR
View the build log or the debug log for each test