Log: Set log level via environment

If the BTOP_LOG_LEVEL is found in the environment it is parsed and
overwrites the current configured log level. The --debug switch still
has precedence

The value of BTOP_LOG_LEVEL must match one of `Logger::log_levels`
fields, being case insensitive

src/btop.cpp

@@ -804,19 +804,27 @@ int main(int argc, char **argv) {
 	}
 
 	//? Config init
-	{	vector<string> load_warnings;
+	{
+		vector<string> load_warnings;
 		Config::load(Config::conf_file, load_warnings);
 
 		if (Config::current_boxes.empty()) Config::check_boxes(Config::getS("shown_boxes"));
 		Config::set("lowcolor", (Global::arg_low_color ? true : not Config::getB("truecolor")));
 
+		const auto log_level_env = Tools::str_to_upper(std::getenv("BTOP_LOG_LEVEL"));
 		if (Global::debug) {
 			Logger::set("DEBUG");
 			Logger::debug("Starting in DEBUG mode!");
 		}
-		else Logger::set(Config::getS("log_level"));
+		else if (v_contains(Logger::log_levels, log_level_env)) {
+			Logger::set(log_level_env);
+			Logger::info("Logger set to {}", log_level_env);
+		}
+		else {
+			Logger::set(Config::getS("log_level"));
+			Logger::info("Logger set to {}", Config::getS("log_level"));
+		}
 
-		Logger::info("Logger set to {}", (Global::debug ? "DEBUG" : Config::getS("log_level")));
 
 		for (const auto& err_str : load_warnings) Logger::warning("{}", err_str);
 	}