ClipboardHistory: Listen for configuration changes

Resize the clipboard history size dynamically by listening for config
changes. This is currently not ideal since we don't have the callbacks
for `Config::Listener::config_i32_did_change`, so for now we are just
taking the string and attempting to convert it to an int.

Userland/Applets/ClipboardHistory/main.cpp

@@ -25,6 +25,7 @@ int main(int argc, char* argv[])
     auto app = GUI::Application::construct(argc, argv);
 
     Config::pledge_domains("ClipboardHistory");
+    Config::monitor_domain("ClipboardHistory");
 
     if (pledge("stdio recvfd sendfd rpath", nullptr) < 0) {
         perror("pledge");