Document LoggerType concept and improve Getting Started chapter

Summary:
related to T15252, T15261, T15263, #24

- documented LoggerType concept
- configuring the client chapter changed to getting started chapter with new additions:
	- code examples for each section (choosing underlying type, configuring the client, and using it)
	- added a secion on debugging the client using our logger implementation
- minor fixes related to reviewer's suggestions

Reviewers: ivica

Reviewed By: ivica

Subscribers: iljazovic, miljen

Differential Revision: https://repo.mireo.local/D32487

example/hello_world_over_tcp.cpp

@@ -15,23 +15,36 @@
 #include <async_mqtt5.hpp>
 
 int main() {
+	//[init_tcp_client
+	// Initialize the execution context required to run I/O operations.
 	boost::asio::io_context ioc;
 
 	// Construct the Client with ``__TCP_SOCKET__`` as the underlying stream.
-	async_mqtt5::mqtt_client<boost::asio::ip::tcp::socket> client(ioc);
+	//async_mqtt5::mqtt_client<boost::asio::ip::tcp::socket> client(ioc);
+	async_mqtt5::mqtt_client<boost::asio::ip::tcp::socket, std::monostate /* TlsContext */, async_mqtt5::logger> client(
+		ioc, {} /* tls_context */, async_mqtt5::logger(async_mqtt5::log_level::debug)
+	);
+	//]
 
+	//[configure_tcp_client
 	// 1883 is the default TCP MQTT port.
 	client.brokers("broker.hivemq.com", 1883)
+		.credentials("async_mqtt5_tester")
 		.async_run(boost::asio::detached);
+	//]
 
+	//[publish_hello_world
 	client.async_publish<async_mqtt5::qos_e::at_most_once>(
 		"async-mqtt5/test", "Hello world!",
 		async_mqtt5::retain_e::yes, async_mqtt5::publish_props {},
 		[&client](async_mqtt5::error_code ec) {
 			std::cout << ec.message() << std::endl;
+
+			// Disconnnect the Client.
 			client.async_disconnect(boost::asio::detached);
 		}
 	);
+	//]
 
 	ioc.run();
 }