resource/aws_cloudformation_stack: Fix perpetual diff on template with transform

[hanazuki]

In refreshing the state of an aws_cloudformation_stack, request the "Original" template body with CFn GetTemplate API to avoid perpetual diff in case the template uses macro transform, such as the AWS::Serverless framework.

ref: https://docs.aws.amazon.com/AWSCloudFormation/latest/APIReference/API_GetTemplate.html

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Fixes #6662

Release note for CHANGELOG:

* resource/aws_cloudformation_stack: Fix perpetual diff on template with transform

Output from acceptance testing:

$ make testacc TESTARGS='-run=TestAccAWSCloudFormationStack_withTransform'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./aws -v -parallel 20 -run=TestAccAWSCloudFormationStack_withTransform -timeout 120m
=== RUN   TestAccAWSCloudFormationStack_withTransform
=== PAUSE TestAccAWSCloudFormationStack_withTransform
=== CONT  TestAccAWSCloudFormationStack_withTransform
--- PASS: TestAccAWSCloudFormationStack_withTransform (58.22s)
PASS
ok      github.com/terraform-providers/terraform-provider-aws/aws       (cached)

[bflad]

Thanks for submitting this, @hanazuki, looks good. 🚀 Thank you for providing that new test case, which does present a perpetual difference without this change.

Output from acceptance testing:

--- PASS: TestAccAWSCloudFormationStack_allAttributes (66.95s)
--- PASS: TestAccAWSCloudFormationStack_basic (65.97s)
--- PASS: TestAccAWSCloudFormationStack_dataSource_basic (65.60s)
--- PASS: TestAccAWSCloudFormationStack_dataSource_yaml (68.56s)
--- PASS: TestAccAWSCloudFormationStack_defaultParams (65.19s)
--- PASS: TestAccAWSCloudFormationStack_disappears (66.83s)
--- PASS: TestAccAWSCloudFormationStack_withParams (114.62s)
--- PASS: TestAccAWSCloudFormationStack_withTransform (43.79s)
--- PASS: TestAccAWSCloudFormationStack_withUrl_withParams (116.98s)
--- PASS: TestAccAWSCloudFormationStack_withUrl_withParams_noUpdate (71.85s)
--- PASS: TestAccAWSCloudFormationStack_withUrl_withParams_withYaml (64.05s)
--- PASS: TestAccAWSCloudFormationStack_yaml (64.69s)

[ghost]

This has been released in version 2.44.0 of the Terraform AWS provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template for triage. Thanks!

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!