[terraform-ibm-landing-zone] Revert provider visibility change and plug test gap

[ocofaigh]

There is a known provider bug (fix is coming in this PR) when setting the provider visibility to private related to resource tags. My understanding is it only happens in some regions. For example, us-east has an issue, but us-south does not.

This is the error you get:

2024/12/09 10:07:38 Terraform plan | Error: ---
 2024/12/09 10:07:38 Terraform plan | id: terraform-e872e09b
 2024/12/09 10:07:38 Terraform plan | summary: "1 error occurred:\n\t* Get \"https://tags.private.us-east.global-search-tagging.cloud.ibm.com/v3/tags?tag_type=access\":
 2024/12/09 10:07:38 Terraform plan |   dial tcp: lookup tags.private.us-east.global-search-tagging.cloud.ibm.com on 172.21.0.10:53:
 2024/12/09 10:07:38 Terraform plan |   no such host\n\n"

The landing zone catalog validation tests are failing with this error, since they tried to deploy to us-east. I think we need to revert the PR #921 until the provider is fixed and new version released.

Ideally we should of caught this in the PR tests, when reverting, can we also ensure that we have at least 1 private test running in schematics, passing a value for tags and running in us-east (its ok to hard code one of the test to use us-east with a code comment linking to this issue)