[Playground] Use impersonate_service_account in Terraform

For security purposes, we need to avoid service account keys in terraform. So that we need to use impersonate_service_account in terraform providers.

Imported from Jira [BEAM-13971](https://issues.apache.org/jira/browse/BEAM-13971). Original Jira may contain additional context.
Reported by: IKozyrev.

Inspect the Playground Terraform configuration and provider definitions to find where service account keys are referenced. Read the original Jira issue for additional context, then determine the required impersonate_service_account setup and verify that the Terraform configuration no longer depends on service account keys.

Written by the indexing model from the issue text.