Introduce a generic GraphQL base resolver

[dnlkoch]

Backport of #221 to the main.

This introduces a BaseGraphQLDataFetcher which registers several base GraphQL queries and mutations (!) once implemented for a given entity (e.g. ApplicationGraphQLDataFetcher). The names of the queries will be autogenerated for each available operation following simple conventions:

• findAll
  • all{BaseEntities}, e.g. allApplications
• findOne
  • {BaseEntity}ById, e.g. applicationById
• create
  • create{BaseEntity}, e.g. createApplication
• update
  • update{BaseEntity}, e.g. updateApplication
• delete
  • delete{BaseEntity}, e.g. deleteApplication

Please see the shogun.graphqls for a full list of available queries and mutations.

Upgrade notes for projects:

• The property shogun.graphql.skipBean is no longer needed and can be removed from the application.yml
• Any custom GraphQLProvider can be removed.
• Any custom data fetcher (registered in the GraphQLProvider) should be moved to a single resolver, e.g.:

@Component
public class MyEntityGraphQLDataFetcher extends BaseGraphQLDataFetcher<MyEntity, MyEntityService> {

    @Autowired
    private MyEntityRepository repository;

    @GraphQLQuery(name = "myEntityBySomething")
    public DataFetcher myEntityBySomething() {
        return dataFetchingEnvironment -> {
            String something = dataFetchingEnvironment.getArgument("something");
            return this.repository.findBySomething(something);
        };
    }
}

(Note the annotation @GraphQLQuery which defines the name of the query which is needed to register it in the schema file.)

Please review @terrestris/devs.

(In addition a new service method for returning the owner an entity has been added.)