Update test to run in schematics and use private provider visability

[ocofaigh]

This DA will no longer deploy since the provider_visability now defaults to private. It fails with:

2024/11/28 18:59:46 Terraform plan | Error: Get "https://private.resource-controller.cloud.ibm.com/v1/resource_keys": dial tcp: lookup private.resource-controller.cloud.ibm.com on 172.21.0.10:53: no such host
 2024/11/28 18:59:46 Terraform plan | 
 2024/11/28 18:59:46 Terraform plan |   with data.ibm_resource_key.elastic_credentials[0],
 2024/11/28 18:59:46 Terraform plan |   on main.tf line 190, in data "ibm_resource_key" "elastic_credentials":
 2024/11/28 18:59:46 Terraform plan |  190: data "ibm_resource_key" "elastic_credentials" {
 2024/11/28 18:59:46 Terraform plan | 
 2024/11/28 18:59:46 Terraform plan | ---
 2024/11/28 18:59:46 Terraform plan | id: terraform-b22cb499
 2024/11/28 18:59:46 Terraform plan | summary: 'Get
 2024/11/28 18:59:46 Terraform plan | "https://private.resource-controller.cloud.ibm.com/v1/resource_keys":
 2024/11/28 18:59:46 Terraform plan |   dial tcp: lookup private.resource-controller.cloud.ibm.com on 172.21.0.10:53: no
 2024/11/28 18:59:46 Terraform plan |   such host'
 2024/11/28 18:59:46 Terraform plan | severity: error
 2024/11/28 18:59:46 Terraform plan | resource: (Data) ibm_resource_key
 2024/11/28 18:59:46 Terraform plan | operation: read
 2024/11/28 18:59:46 Terraform plan | component:
 2024/11/28 18:59:46 Terraform plan |   name: github.com/IBM-Cloud/terraform-provider-ibm
 2024/11/28 18:59:46 Terraform plan |   version: 1.71.2
 2024/11/28 18:59:46 Terraform plan | ---

I have created a provider issue to track this: IBM-Cloud/terraform-provider-ibm#5828

However the tests in this module should of caught this, but it seems all the tests are overriding the default back to provider_visability = public so hence we didnt catch the error.
We need at least 1 test that keeps this as private - meaning that test will need to run in schematics.

We also need to ensure we have a test that would actually catch this use case. It looks like to reproduce, a value needs to be passed for elastic_instance_crn.

As a temporary workaround, the DA has been reverted to use public in #234