regional availability of hosted transforms

## 1. Title
[`AWS::Include`](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/create-reusable-transform-function-snippets-and-add-to-your-template-with-aws-include-transform.html) in `us-iso-east-1`, `us-isob-east-1`, `ap-northeast-3`, ~`us-gov-east-1`~, ~`cn-north-1`~ and ~`cn-northwest-1`~

## 5. Helpful Links to speed up research and evaluation
Background: We are using DefinitionBody in AWS::ApiGateway::RestApi resource to specify API definition. [`AWS::Include`](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/create-reusable-transform-function-snippets-and-add-to-your-template-with-aws-include-transform.html) allows storing the API definition file in S3 when it is very big while we can still take advantages of CloudFormation intrinsics functions in API definition file such as the Lambda ARN

Start with the linked AWS::Include documentation and the AWS::ApiGateway::RestApi DefinitionBody context described in the issue. Confirm the requested regional availability for us-iso-east-1, us-isob-east-1, and ap-northeast-3; done means the availability request has a clear resolution for those regions.

Written by the indexing model from the issue text.