GR 1 and 2: Implement SSO for Super Admin and at Identity org level for Evidence ATO acceptance

[fmichaelobrien]

We currently perform SSO for the super admin and the identity organization to adhere to GR 1 and 2 evidence requirements. This should be formalized in the repo readme manual instructions References https://github.com/GoogleCloudPlatform/pbmm-on-gcp-onboarding/blob/main/docs/google-cloud-security-controls.md#guardrails-evidence-package https://github.com/GoogleCloudPlatform/pbmm-on-gcp-onboarding/blob/main/docs/google-cloud-security-controls.md#01-protect-root--global-admins-account https://github.com/GoogleCloudPlatform/pbmm-on-gcp-onboarding/blob/main/docs/google-cloud-security-controls.md#02-management-of-administrative-privileges https://github.com/GoogleCloudPlatform/pbmm-on-gcp-onboarding/blob/main/docs/google-cloud-security-controls.md#iam---mfa https://github.com/GoogleCloudPlatform/pbmm-on-gcp-onboarding/blob/main/docs/google-cloud-security-controls.md#iam---mfa---mfa-on-super-admin-account https://github.com/GoogleCloudPlatform/pbmm-on-gcp-onboarding/blob/main/docs/google-cloud-security-controls.md#iam---mfa---mfa-on-entire-organization-level