Future-proofing generated types

[rafalp]

One of our teams at Mirumee would like to future-proof their generated client.

They already know how the GraphQL API they are integrating with will change in future and would like the generated client to already target the future API, but include the backwards compat layer.

Initial idea for solving this would be implementing a plugin that adds mapping in generated client methods from current objects reps to old ones, but this requires further study before we can make a decision about implementing something in codegen/plugin or just offering a general recommendation.