Add TrivalDataFetcher Marker interface

[cliedeman]

None of the datafetchers created implement the TrivalDataFetcher interface so they show up in instrumentation code.

https://github.com/graphql-java-kickstart/graphql-java-tools/blob/master/src/main/kotlin/com/coxautodev/graphql/tools/MethodFieldResolver.kt#L108

We could add another check here with a heuristic to see if we think we have a trivial data fetcher:

• 0 arguments
• The method in question in on the search.type or a parent class
• The method starts with get