add subject_id to transfer job project SA

[DrFaust92]

Add subject_id attribute to the transfer job project SA data source, this will allow getting the subject id to create aws iam role assumable by google SA and reduce the need to static IAM keys on AWS side.

Closes hashicorp/terraform-provider-google#11149

If this PR is for Terraform, I acknowledge that I have:

• 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).
• Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
• 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).
• Ran relevant acceptance tests (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)

transfer: added attribute `subject_id` to data source `google_storage_transfer_project_service_account`

[modular-magician]

Hello! I am a robot who works on Magic Modules PRs.

I have detected that you are a community contributor, so your PR will be assigned to someone with a commit-bit on this repo for initial review.

Thanks for your contribution! A human will be with you soon.

@shuyama1, please review this PR or find an appropriate assignee.

[shuyama1]

/gcbrun

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 3 files changed, 11 insertions(+), 1 deletion(-))
Terraform Beta: Diff ( 3 files changed, 11 insertions(+), 1 deletion(-))
TF Validator: Diff ( 2 files changed, 3 insertions(+), 3 deletions(-))

[modular-magician]

I have triggered VCR tests in RECORDING mode for the following tests that failed during VCR: TestAccDataSourceGoogleStorageTransferProjectServiceAccount_basic|TestAccDatasourceGoogleServiceNetworkingPeeredDnsDomain_basic|TestAccApigeeEnvironmentIamBindingGenerated|TestAccApigeeEnvironmentIamMemberGenerated|TestAccApigeeEnvironmentIamPolicyGenerated|TestAccCloudbuildWorkerPool_basic|TestAccComputeForwardingRule_update|TestAccContainerCluster_withAuthenticatorGroupsConfig|TestAccServiceNetworkingPeeredDNSDomain_basic You can view the result here: https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=261050

[shuyama1]

LGTM! Failing tests seem unrelated. Thank you!