private static void populateConfigBuilder(Builder builder, ConfigProducer configProducer) {
        boolean found = configProducer.cascadeConfig(builder);
        boolean foundOverride = configProducer.addUserConfig(builder);
        log.log(Level.FINE, () -> "Trying to get config for " + builder.getClass().getDeclaringClass().getName() +
                                  " for config id " + quote(configProducer.getConfigId()) +
                                  ", found=" + found + ", foundOverride=" + foundOverride);
    }
Resolves config for a given config id and populates the given builder with the config.

@param builder a configinstance builder
@param configId the config id for the config client
@return the builder if a producer was found, and it did apply config, null otherwise
config-model/src/main/java/com/yahoo/vespa/model/VespaModel.java