[v2] Implement a CLI

[Maximilien-R]

In order to improve the developer experience, it could be interesting to develop a CLI dedicated to tartiflette.

This CLI could integrate a certain number of built-in commands, but it should be easy to extend using a third party package. A quick and easy solution to implement could be to rely on click which allows the extension relatively easily.

The CLI could provide many tools such as:

• validate an SDL or a request (by providing a file / folder)
• determine if the evolution of an SDL presents break changes
• generate Python code (resolvers, directives, scalars ...) from an SDL
• generate SDL interactively
• generate SQLAlchemy models from an SDL
• ...