Add support for AutoScaling Scaling Policy Import

[teraken0509]

Fixes #6578

Changes proposed in this pull request:

• Add import support for aws_autoscaling_policy

Output from acceptance testing:

$ make testacc TEST=./aws TESTARGS='-run=TestAccAWSAutoscalingPolicy_basic'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./aws -v -parallel 20 -run=TestAccAWSAutoscalingPolicy_basic -timeout 120m
=== RUN   TestAccAWSAutoscalingPolicy_basic
=== PAUSE TestAccAWSAutoscalingPolicy_basic
=== CONT  TestAccAWSAutoscalingPolicy_basic
--- PASS: TestAccAWSAutoscalingPolicy_basic (95.48s)
PASS
ok  	github.com/terraform-providers/terraform-provider-aws/aws	95.539s

[bflad]

FYI this was good but when expanding the acceptance testing to run ImportState steps for the rest of the test resources, I found that step_adjustment was failing to properly be read into the Terraform state and submitted this followup: #7336

[bflad]

This has been released in version 1.57.0 of the AWS provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

[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!