private FileDownloader createDownloader(Supervisor supervisor, ConfigSourceSet source) {
        return new FileDownloader(new FileDistributionConnectionPool(source, supervisor),
                                  supervisor,
                                  Duration.ofSeconds(55)); // Should be lower than the timeout in FileAcquirer
    }
Keeps track of file distribution and url download rpc servers.

@author hmusum
config-proxy/src/main/java/com/yahoo/vespa/config/proxy/filedistribution/FileDistributionAndUrlDownload.java