print config vars to console #101

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impl Config {
    pub fn new() -> anyhow::Result<Config> {
        let mut config = config::Config::default();

        if std::path::Path::new("config.toml").exists() {
            config.merge(config::File::with_name("config")).unwrap();
        }

        update_from_env(&mut config);

        if config.get::<u16>("port").is_err() {
            config.set("port", 4347).unwrap();
        }

        // TODO: print resulted config (perfectly, it needs adding `derive(Debug)` in `subbeat`'s `DatasourceConfig`)
        Ok(Config {
            port: config.get::<u16>("port").unwrap(),
            datasource_config: resolve_datasource(&config)?,
            alerting: resolve_alerting(&config)?,
        })
    }
}

so this issue is about printing to log (console) variables values