resource/aws_appautoscaling_target: Support updating max_capacity, min_capacity, and role_arn attributes

[bflad]

This is a simplified remake of the #2542 PR after the IAM service role changes that needed to get in as part of #2889. The basic test already handles updating the max/min capacities and checking their values in state, hence why no test changes for them. Adding a check for IAM role updates I think is a can of worms given the weird IAM service role half state in AWS at this point.

The RegisterScalableTarget API call supports updating attributes on existing targets.

Closes #240 and potentially #968

make testacc TEST=./aws TESTARGS='-run=TestAccAWSAppautoScalingTarget'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./aws -v -run=TestAccAWSAppautoScalingTarget -timeout 120m
=== RUN   TestAccAWSAppautoScalingTarget_basic
--- PASS: TestAccAWSAppautoScalingTarget_basic (45.26s)
=== RUN   TestAccAWSAppautoScalingTarget_spotFleetRequest
--- PASS: TestAccAWSAppautoScalingTarget_spotFleetRequest (67.99s)
=== RUN   TestAccAWSAppautoScalingTarget_emrCluster
--- PASS: TestAccAWSAppautoScalingTarget_emrCluster (499.71s)
=== RUN   TestAccAWSAppautoScalingTarget_multipleTargets
--- PASS: TestAccAWSAppautoScalingTarget_multipleTargets (31.47s)
=== RUN   TestAccAWSAppautoScalingTarget_optionalRoleArn
--- PASS: TestAccAWSAppautoScalingTarget_optionalRoleArn (25.98s)
PASS
ok  	github.com/terraform-providers/terraform-provider-aws/aws	670.459s

[catsby]

👍

[bflad]

This has been released in terraform-provider-aws version 1.8.0. 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!