provider: Infer AWS partition from configured region

[bflad]

Fixes part of #3045

Regions are part of an AWS partition and the AWS SDK endpoints package provides the functionality to determine the partition from the configured region name. We do not need the account ID fetching process (optionally skippable in the provider) to grab the partition.

make testacc TEST=./aws TESTARGS='-run=TestAccAWSS3Bucket_basic'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./aws -v -run=TestAccAWSS3Bucket_basic -timeout 120m
=== RUN   TestAccAWSS3Bucket_basic
--- PASS: TestAccAWSS3Bucket_basic (26.21s)
PASS
ok  	github.com/terraform-providers/terraform-provider-aws/aws	26.254s

[catsby]

👍

[terraform-provider-aws][pr-3173]$ go test ./aws/... -run="TestAWSGetAccount"
ok      github.com/terraform-providers/terraform-provider-aws/aws       0.046s

[bflad]

This has been released in terraform-provider-aws version 1.9.0. 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!