The various GraphQL clients supported in this project automatically detect
JSON codecs for reading/writing GraphQL requests as JSON payloads.
If there is none detected, clients provide a default codec instance.
This commit configures automatically the `GraphQlModule` from gh-1174 in
default codecs and add integration tests for `FieldValue<T>` usage on the
client side.
This also improves the documentation around `FieldValue<T>` for both
server and client side support.
Closes gh-1190
70f16c1158