Add Spring GraphQL support

[bclozel]

Now that the Spring GraphQL project has made significant project in its Milestone phase, we should move the experimental auto-configuration and starter in this project.

We should address the following tasks:

• Add dependency management for Spring GraphQL and GraphQL Java
• Auto-configure Spring GraphQL base infrastructure
• Add a FailureAnalyzer for InvalidSchemaLocationsException
• Auto-configure HTTP transport for MVC and WebFlux
• Auto-configure schema printer and graphiql endpoints
• Auto-configure CORS options for GraphQL web endpoints
• Auto-configure GraphQL WebSocket endpoint
• Auto-configure Query* support for GraphQL
• Auto-configure security for Spring GraphQL
• Add testing support with GraphQlTester and @GraphQlTest
• Add Metrics support
• Create Spring Boot starter

See spring-projects/spring-graphql#207