Upgrade graphql-java to version 14

[vojtapol]

graphql-java version 14 has been released.

It would be great if someone could upgrade the dependency and test that everything works.

[lburja]

I've created a pull request.
I don't know Kotlin very well, so maybe there is a more elegant way to solve the compilation issue caused by graphql-java 14. In any case, the result works fine on a medium-large application.

[lburja]

Any timeline for merging this?