Add c5a, c6g, and r6g to instance types in constants
Add c5a, c6g, and r6g to instance types in constants

See
- https://aws.amazon.com/blogs/aws/new-m6g-ec2-instances-powered-by-arm-based-aws-graviton2/
- https://aws.amazon.com/blogs/aws/new-amazon-ec2-c5a-instances-powered-by-2nd-gen-amd-epyc-processors/
- https://aws.amazon.com/ec2/instance-types/

cloudtools/troposphere,cloudtools/troposphere