Prior to this commit, the `GraphQlHttpHandler` implementations would use
the JSON codecs configured in the web Framework (MVC or WebFlux) for
reading and writing GraphQL payloads as JSON documents.
This can cause issues in cases the application configures the JSON codec
in a way that makes it incompatible with the expected GraphQL documents.
For example, not serializing empty values and arrays.
This commit adds new constructors in `GraphQlHttpHandler`
implementations that can get a custom JSON codec for GraphQL payloads.
Closes gh-860
9e4d77395a