stack_set.operation_preferences.failure_tolerance_count can be zero

[MarkCBell]

Currently, an aws_cloudformation_stack_set with:

  operation_preferences {
    failure_tolerance_count = 0
    max_concurrent_percentage = 100
  }

fails with Validation Error: Exactly one of FailureTolerancePercentage and FailureToleranceCount must be specified since both parameters are present. This is because currently the FailureToleranceCount and FailureTolerancePercentage attributes are both set (possibly to a default value of 0) and then one is removed if it is zero and the other is non-zero. Therefore with the operation_preferences block above both remain, leading to the Validation Error being raised. This PR removes the requirement that the other be non-zero and so allows the above operation_preferences block to work.

Note that although this does not apply to max_concurrent_percentage / max_concurrent_count since at least one of these must be at least one, I propose making the same change there just to keep the logic the same.

[ewbankkit]

LGTM 🚀.

% make testacc TESTS=TestAccCloudFormationStackSet_operationPreferences PKG=cloudformation
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./internal/service/cloudformation/... -v -count 1 -parallel 20 -run='TestAccCloudFormationStackSet_operationPreferences'  -timeout 180m
=== RUN   TestAccCloudFormationStackSet_operationPreferences
=== PAUSE TestAccCloudFormationStackSet_operationPreferences
=== CONT  TestAccCloudFormationStackSet_operationPreferences
--- PASS: TestAccCloudFormationStackSet_operationPreferences (125.20s)
PASS
ok  	github.com/hashicorp/terraform-provider-aws/internal/service/cloudformation	128.933s

[ewbankkit]

@MarkCBell Thanks for the contribution 🎉 👏.

[github-actions]

This functionality has been released in v4.11.0 of the Terraform AWS Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

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[github-actions]

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