Support for Transit Gateway Peers in the Routes: section.

[apmclean]

Is your feature request related to a problem? Please describe.
When a peer transit gateway is created you must manage the VPC routes to that Transit Gateway manually.

Describe the solution you'd like
Ability to model a Transit Gateway Peer Attachment in the configuration file and be able to use it in the 'routes' section as a destination.

Describe alternatives you've considered
None

Additional context
None

Could you submit a PR to implement this feature?
Yes