Feature: add automatic key creation

[Plazide]

This is a planned feature.

When making frontend applications, you usually need to have public keys that non-authenticated users can use to send requests to the GraphQL API.

This feature would create those keys if they don't exist, and log them for the developer to put into an environment variable. Alternatively (or additionally), this secret would be automatically written to the environment and environment file. The name of the environment variable would be editable through an option in .fauna.json.

This is often a one-time task for each project, but for people who create multiple projects in quick succession (ie. me) this would make the setup slightly easier. It would also make it easier to set up the same database for production; automating a step.