Add validation to targets for aws_route

[gdavison]

Description

The aws_route resource allows practitioners to incorrectly add more than one target type, when only one can be used. tflint has added a check to prevent this, but we should implement it in the provider.

Use ExactlyOneOf, since one of the targets is required.

New or Affected Resource(s)

• aws_route

[ewbankkit]

We should also be able to do this for destination type destination_cidr_block and destination_ipv6_cidr_block (and destination_prefix_list_id for #13986).

The TestAccAWSRoute_ConditionalCidrBlock acceptance test case fails if ExactlyOneOf is applied to destination_cidr_block and destination_ipv6_cidr_block. This can be enabled once #13943 is addressed.

[ghost]

This has been released in version 3.34.0 of the Terraform AWS provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template for triage. Thanks!

[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!