TransitGateway not returning the default route table ID

### Name of the resource

AWS::EC2::TransitGateway

### Resource name

_No response_

### Description

TransitGateway is not returning the default routing table so it's not possible to add additional route to the default route table when the TGW is created.

### Other Details

https://github.com/aws/aws-cdk/issues/24473#issuecomment-1461085588

Start with the AWS::EC2::TransitGateway resource and review the linked AWS CDK discussion for the expected default route table behavior. Confirm how the default routing table ID should be exposed; done means the created transit gateway returns that ID so an additional route can be added to the default route table.

Written by the indexing model from the issue text.