Allow control over running it in a separate thread

[ABeltramo]

First off, thanks for this brilliant library!

A user recently introduced this library into my open source project wolf and everything seems to be working, expect for when it doesn't 😅

A user reported the following exception:

mDNS: Local IPv4 address: 192.168.178.25
mDNS: Local IPv6 address: fd30:854e:2d95:0:e9d:92ff:fe84:f3a9
mDNS: Error: Failed to open any client sockets

I'm not sure what's causing it (any help in debugging that?) but when you throw from your thread I have no way to catch those exceptions from the main thread.
So I've added a simple bool flag to avoid starting that thread automatically and instead do something like:

  std::thread([]() {
    logs::log(logs::info, "Starting mDNS service");
    try {
      // ...
      mdns.startService(false);
    } catch (const std::exception &e) {
      logs::log(logs::error, "mDNS error: {}", e.what());
    }
  }).detach();

To avoid crashing the main application when that fails.

Let me know what you think!