CLI tests for logging flags (#3609)

## Issue Addressed
Adding CLI tests for logging flags: log-color and disable-log-timestamp
Which issue # does this PR address?
#3588 
## Proposed Changes
Add CLI tests for logging flags as described in #3588 
Please list or describe the changes introduced by this PR.
Added logger_config to client::Config as suggested. Implemented Default for LoggerConfig based on what was being done elsewhere in the repo. Created 2 tests for each flag addressed.
## Additional Info

Please provide any additional information. For example, future considerations
or information useful for reviewers.

lcli/src/main.rs

@@ -781,8 +781,8 @@ fn run<T: EthSpec>(
         .map_err(|e| format!("should start tokio runtime: {:?}", e))?
         .initialize_logger(LoggerConfig {
             path: None,
-            debug_level: "trace",
-            logfile_debug_level: "trace",
+            debug_level: String::from("trace"),
+            logfile_debug_level: String::from("trace"),
             log_format: None,
             log_color: false,
             disable_log_timestamp: false,