Add GraphQL layer

[pereiren]

Hi,

First of all thank you very much for this awesome work @ivanpaulovich and contributors.

I would love to see a GraphQL API co-existing with the current API.

Actually there are 2 big libraries in the .NET Core GraphQL community:

• graphql-dotnet https://github.com/graphql-dotnet/graphql-dotnet
• HotChocolate https://github.com/ChilliCream/hotchocolate

I have tested both of them and personally I do prefer HotChocolate, and even having a smaller comunnity I think they are releasing new features faster and documentation is (at least for me) much clearer.

I would love to collaborate on this trying to integrate GraphQL following the clean architecture approach.

Just let me know if you think it would be ok :)

Thanks in advance!