Add support for EndpointConfiguration.IpAddressType for REST APIs and Custom Domains

[txase]

Description

I want to deploy a dual-stack (IPv4 / IPv6) API Gateway REST API and Custom Domain. This requires setting the AWS::ApiGateway::RestApi resource's EndpointConfiguration.IpAddressType and Domain.EndpointConfiguration.IpAddressType properties to 'dualstack'. However, the SAM transform is silently ignoring these options when provided in AWS::Serverless::Api

Steps to reproduce

Create an API with the following configuration:

Resources:
  Api:
    Type: AWS::Serverless::Api
    Properties:
      Name: my-api
      StageName: Prod
      DefinitionBody:
        openapi: 3.0.1
        info:
          title: my-api
          version: 1
        paths:
          /{proxy+}:
            x-amazon-apigateway-any-method:
              x-amazon-apigateway-integration:
                httpMethod: POST
                type: aws_proxy
                uri: !Sub arn:${AWS::Partition}:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${APIFunc.Arn}/invocations
              responses: {}
      Domain:
        DomainName: !Sub mydomain.example.com
        CertificateArn: !Ref ApiCertificate
        EndpointConfiguration:
          IpAddressType: dualstack
          Types:
            - REGIONAL
        Route53:
          HostedZoneId: !Ref HostedZoneId
      EndpointConfiguration:
        Type: REGIONAL
        IpAddressType: dualstack

Observed result

A Regional REST API and Custom Domain are created with only IPv4 support. Looking at the processed template, the IpAddressType properties is silently dropped during transformation.

Expected result

Regional, dual-stack REST API and Custom Domains are created.

Additional environment details

1. OS: N/A
2. If using the SAM CLI, sam --version: Not using SAM CLI
3. AWS region: us-west-2