Add graphql-sunset

[sophiabits]

[URL to the resource here.]
https://github.com/sophiabits/graphql-sunset

[Explain what this resource is all about and why it should be included here.]
Sunset is a standard HTTP header used to communicate that a resource will become unavailable in future. This signaling is important as it gives consumers warning for them to move off the deprecated resource before removal, and because the Sunset header is interpretable programmatically consumers can build nice alerting systems around it (WeWork has done this, for instance: https://github.com/wework/faraday-sunset)

This library offers a simple and easy way to add support for this header to GraphQL servers. Schema resources can be annotated with an @sunset directive, and the server will automatically send back a Sunset response header to any consumer that requests those marked resources.