public void useFeatureFlags(ModelContext.FeatureFlags featureFlags) {
        this.useV8GeoPositions = featureFlags.useV8GeoPositions();
    }
Creates and initializes a new Vespa from the service config file
in the given application directory.

@param parent the parent, usually VespaModel
@param name   the name, used as configId
@param documentModel DocumentModel to serve global document config from.
config-model/src/main/java/com/yahoo/config/model/ApplicationConfigProducerRoot.java