Add CLI flag to opt in to world-readable log files (#3747)

## Issue Addressed

#3732

## Proposed Changes

Add a CLI flag to allow users to opt out of the restrictive permissions of the log files.

## Additional Info

This is not recommended for most users. The log files can contain sensitive information such as validator indices, public keys and API tokens (see #2438). However some users using a multi-user setup may find this helpful if they understand the risks involved.

lcli/src/main.rs

@@ -789,6 +789,7 @@ fn run<T: EthSpec>(
             max_log_size: 0,
             max_log_number: 0,
             compression: false,
+            is_restricted: true,
         })
         .map_err(|e| format!("should start logger: {:?}", e))?
         .build()