Facilitate comments in GraphQL schema generation flow

[tsilvasstk]

Is your feature request related to a problem? Please describe.
The GraphQL schema that is generated has no comments/documentation. It does not suit inclusion into a well documented federated graph.

Describe the solution you'd like
A way to annotate dimensions such that the generated GraphQL types have some degree of documentation.

Describe alternatives you've considered
Manual documentation post-generation. It does not suit our needs as we scale up

[paveltiunov]

@tsilvasstk I guess we can use the description to generate comments. Thanks for posting it! Please let us know if you want to work on this!

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[igorlukanin]

It looks like this might require a fairly tiny change to this part of code: https://github.com/cube-js/cube/blob/master/packages/cubejs-api-gateway/src/graphql.ts#L378-L398