expand valid values for bigquery dataset

[ScottSuarez]

fixes bug where validation added for iam member was breaking previously valid configurations
closes hashicorp/terraform-provider-google#13484

Bigquery has a special subset of member allowances... projectReaders, projectOwners, projectWriters
https://cloud.google.com/bigquery/docs/reference/rest/v2/datasets

Release Note Template for Downstream PRs (will be copied)

bigquery:  fixed bug where valid iam member values for bigquery were prevented from actuation by validation

[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 ( 1 file changed, 1 insertion(+), 1 deletion(-))
Terraform Beta: Diff ( 1 file changed, 1 insertion(+), 1 deletion(-))
TF Validator: Diff ( 2 files changed, 3 insertions(+), 3 deletions(-))

[modular-magician]

Tests analytics

Total tests: 2423
Passed tests 2170
Skipped tests: 252
Failed tests: 1

Action taken

Triggering VCR tests in RECORDING mode for the tests that failed during VCR. Click here to see the failed tests

TestAccRegionInstanceGroupManager_stateful

[modular-magician]

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

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