Add AWS::MediaPackage per 2020-10-22 changes

[markpeek]

Currently invalid resource spec for this component.

The following resources were added: AWS::MediaPackage::Asset, AWS::MediaPackage::Channel, , AWS::MediaPackage::OriginEndpoint, AWS::MediaPackage::PackagingConfiguration, and AWS::MediaPackage::PackagingGroup.

AWS::MediaPackage::Asset.
Use the AWS::MediaPackage::Asset to specify an asset to ingest VOD content.

AWS::MediaPackage::Channel.
Use the AWS::MediaPackage::Channel to specify a channel to receive content.

AWS::MediaPackage::OriginEndpoint.
Use the AWS::MediaPackage::OriginEndpoint to specify an endpoint on an AWS Elemental MediaPackage channel.

AWS::MediaPackage::PackagingConfiguration.
Use the AWS::MediaPackage::PackagingConfiguration to specify a packaging configuration in a packaging group.

AWS::MediaPackage::AWS::MediaPackage::PackagingGroup.
Use the AWS::MediaPackage::PackagingGroup to specify a packaging group.