Add GraphQL Support

[danehans]

GraphQL is becoming a common approach for aggregating queries from frontends to backend services. TID should provide GraphQL support, initially focusing on Istio Ingress Gateway.

Potential Work Items:

1. Define an API, e.g. CRD, for configuring/managing a GraphQL implementation, i.e. Apollo, but not lock the API to a specific implementation.
2. Allow developers to store GraphQL schemas as code, observe usage and publish information.
3. Create a GraphQL schema generator. Consider using the TSB OpenAPI generator as a reference implementation for the GraphQL schema generator.

cc: @zinuga

[danehans]

An example of integrating Apollo with Istio ingress:

https://itnext.io/istio-service-mesh-apollo-server-for-graphql-7e7421fce5d0