lightway-client log level can not directly change in command line

[yanganto]

Hi,
Before on-boarding, I try to play with lightway with my machines, and find out a possible issue on configure ordering. In case I forgot it, so I list down here and nothing urgent.

If there is any other consideration behind this, and this is not an issue, it will be nice to close it. If there is something I can do, I will be happy to go on this issue.

The previous configure order are

1. option of cli
2. environment variable
3. config file

managed by following code.

lightway/lightway-client/src/main.rs

Lines 75 to 79 in 08d8038

	let mut config = Config::with_layers(&[
	Layer::Yaml(config_file.to_owned()),
	Layer::Env(Some(String::from("LW_CLIENT_"))),
	Layer::Clap(matches),
	])?;

---

After the code increasing change in this month, the order will be a little be confused, because there are two environment variable do the same thing but different order. Besides, it is counter-intuitive, the cli option --log-level will be override by environment variable.

1. environment variable(RUST_LOG)
2. default directive (currently unset)
3. option of cli
4. environment variable(LW_CLIENT_LOG_LEVEL)
5. config file (log_level field)

managed by following code.

lightway/lightway-client/src/main.rs

Lines 81 to 90 in 08d8038

	let filter = tracing_subscriber::EnvFilter::builder()
	// https://docs.rs/tracing-subscriber/latest/tracing_subscriber/filter/struct.Builder.html#method.with_regex
	// recommends to disable REGEX when using envfilter from untrusted sources
	.with_regex(false)
	.from_env()
	.unwrap_or_else(|_| {
	// If RUST_LOG is not set, use config.log_level as default
	let level: tracing::level_filters::LevelFilter = config.log_level.into();
	tracing_subscriber::EnvFilter::new(level.to_string())
	});

[kp-mariappan-ramasamy]

Thanks for finding the issue.

Yes, it is a bug introduced when I added support for RUST_LOG and it is not intentional to deprecate log-level.

Earlier, we supported only log-level (debug, trace etc) using config cli (and env variable).
It allowed us to set the log level globally.

But when we want to debug an issue and focus on one module trace, it is inconvenient to go through traces from all modules.
Using EnvFilter allows us to create complex logging filters and enable trace for one module.

For normal use cases, log-level which is part of CLI args should be sufficient to change global log level.
And RUST_LOG can be used when we want to debug particular issue.

This PR #331 should fix the bug I introduced.
The behavior will be consistent now.

Please check once the PR is merged