Add arn for aws_subnet and data.aws_subnet

[blckct]

Changes proposed in this pull request:

• Add ARN attribute to aws_subnet and data.aws_subnet
• Update documentation

Output from acceptance testing:

make testacc TESTARGS='-run=TestAccDataSourceAwsSubnet_basic'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./... -v -run=TestAccDataSourceAwsSubnet_basic -timeout 120m
?   	github.com/terraform-providers/terraform-provider-aws	[no test files]
=== RUN   TestAccDataSourceAwsSubnet_basic
--- PASS: TestAccDataSourceAwsSubnet_basic (63.62s)
PASS
ok  	github.com/terraform-providers/terraform-provider-aws/aws	63.640s

make testacc TESTARGS='-run=TestAccAWSSubnet_basic'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./... -v -run=TestAccAWSSubnet_basic -timeout 120m
?   	github.com/terraform-providers/terraform-provider-aws	[no test files]
=== RUN   TestAccAWSSubnet_basic
--- PASS: TestAccAWSSubnet_basic (58.69s)
PASS
ok  	github.com/terraform-providers/terraform-provider-aws/aws	58.711s

[bflad]

LGTM, thanks @blckct! 🚀

9 tests passed (all tests)
=== RUN   TestAccAWSSubnet_importBasic
--- PASS: TestAccAWSSubnet_importBasic (12.91s)
=== RUN   TestAccAWSSubnet_basic
--- PASS: TestAccAWSSubnet_basic (13.11s)
=== RUN   TestAccDataSourceAwsSubnetIDs_filter
--- PASS: TestAccDataSourceAwsSubnetIDs_filter (18.41s)
=== RUN   TestAccAWSSubnet_enableIpv6
--- PASS: TestAccAWSSubnet_enableIpv6 (20.02s)
=== RUN   TestAccDataSourceAwsSubnet_ipv6ByIpv6Filter
--- PASS: TestAccDataSourceAwsSubnet_ipv6ByIpv6Filter (22.22s)
=== RUN   TestAccDataSourceAwsSubnetIDs
--- PASS: TestAccDataSourceAwsSubnetIDs (23.32s)
=== RUN   TestAccDataSourceAwsSubnet_basic
--- PASS: TestAccDataSourceAwsSubnet_basic (26.60s)
=== RUN   TestAccAWSSubnet_ipv6
--- PASS: TestAccAWSSubnet_ipv6 (29.31s)
=== RUN   TestAccDataSourceAwsSubnet_ipv6ByIpv6CidrBlock
--- PASS: TestAccDataSourceAwsSubnet_ipv6ByIpv6CidrBlock (34.07s)

[bflad]

This has been released in version 1.32.0 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!