fix: Add toUpperCase to provider and region fields in cluster resources

[andreaangiolillo]

Description

Ticket: https://jira.mongodb.org/browse/CLOUDP-222427

This PR adds a validation to the provider_name and region_name fields of the cluster resources to return an error if the user did not provide the uppercase string.

Type of change:

• Bug fix (non-breaking change which fixes an issue). Please, add the "bug" label to the PR.
• New feature (non-breaking change which adds functionality). Please, add the "enhancement" label to the PR.
• Breaking change (fix or feature that would cause existing functionality to not work as expected). Please, add the "breaking change" label to the PR.
• This change requires a documentation update
• Documentation fix/enhancement

Required Checklist:

• I have signed the MongoDB CLA
• I have read the contribution guidelines
• I have checked that this change does not generate any credentials and that they are NOT accidentally logged anywhere.
• I have added tests that prove my fix is effective or that my feature works per HashiCorp requirements
• I have added any necessary documentation (if appropriate)
• I have run make fmt and formatted my code
• If changes include deprecations or removals, I defined an isolated PR with a relevant title as it will be used in the auto-generated changelog.

Testing

I added the unit test TestStringIsUppercase

Running tool: /Users/andrea.angiolillo/.asdf/shims/go test -timeout 300000s -run ^TestStringIsUppercase$ github.com/mongodb/terraform-provider-mongodbatlas/internal/service/advancedcluster

ok  	github.com/mongodb/terraform-provider-mongodbatlas/internal/service/advancedcluster	0.776s

[marcosuma]

thanks Andrea!
Question: do we really need one more e2e test for this? Why don't we simply unit test this?

My rationale is: the only business logic that we are responsible for is StringIsUppercase; because of that, unit test should suffice. The added value that an e2e can bring here is that we are effectively confirming ValidateDiagFunc method is correctly called.. but that should not be our responsibility and we should trust our framework that will do so.

Happy to discuss more about this (I am thinking this from a "invert the test pyramid" perspective)

[andreaangiolillo]

Good point. I will update the PR. Thanks!

[andreaangiolillo]

Updated

[AgustinBettati]

LGTM