fix appconfig configuration version drift on each run

[KyMidd]

Rollback Plan

If a change needs to be reverted, we will publish an updated version of the library.

Description

Fixes persistent drift detection in aws_appconfig_hosted_configuration_version when using AppConfig feature flags. AWS AppConfig automatically injects _createdAt and _updatedAt timestamp metadata fields into feature flag configurations at the flags.* and values.* levels, which are not present in the Terraform configuration. This causes Terraform to incorrectly detect drift on every plan/apply cycle, even when no actual changes have been made.

Example Drift Scenario (Before Fix)

  resource "aws_appconfig_hosted_configuration_version" "example" {
    application_id           = aws_appconfig_application.example.id
    configuration_profile_id = aws_appconfig_configuration_profile.example.id
    content_type             = "application/json"

    content = jsonencode({
      flags = {
        feature_flag = {
          name = "featureFlag"
        }
      }
      values = {
        feature_flag = {
          _variants = [
            { enabled = true, name = "Default" }
          ]
        }
      }
    })
  }

After initial apply, subsequent terraform plan would show drift due to AWS adding:

  "flags": {
    "feature_flag": {
      "_createdAt": "2025-10-28T19:14:35.761Z",  // Injected by AWS
      "_updatedAt": "2025-10-28T19:09:00.981Z",  // Injected by AWS
      "name": "featureFlag"
    }
  }

Relations

n/a

References

n/a

Output from Acceptance Testing

Acceptance tests pass:
>  make testacc TESTS=TestAccAppConfigHostedConfigurationVersion PKG=appconfig
  === RUN   TestAccAppConfigHostedConfigurationVersion_basic
  --- PASS: TestAccAppConfigHostedConfigurationVersion_basic (24.25s)
  === RUN   TestAccAppConfigHostedConfigurationVersion_disappears
  --- PASS: TestAccAppConfigHostedConfigurationVersion_disappears (21.48s)
  === RUN   TestAccAppConfigHostedConfigurationVersion_featureFlagsNoDrift
  --- PASS: TestAccAppConfigHostedConfigurationVersion_featureFlagsNoDrift (30.35s)
  PASS
  ok  	github.com/hashicorp/terraform-provider-aws/internal/service/appconfig	63.710s

[github-actions]

✅ Thank you for correcting the previously detected issues! The maintainers appreciate your efforts to make the review process as smooth as possible.

[github-actions]

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