test: change the `existing_kms_instance_guid` to use us-south hpcs and add auth policy for service credential#275

ocofaigh merged 6 commits intomainterraform-ibm-modules/terraform-ibm-secrets-manager:mainfrom

Aashiq-J-patch-1terraform-ibm-modules/terraform-ibm-secrets-manager:Aashiq-J-patch-1Copy head branch name to clipboard