Button device class (#2835)

esphome/components/button/button.cpp

@@ -17,5 +17,12 @@ void Button::press() {
 void Button::add_on_press_callback(std::function<void()> &&callback) { this->press_callback_.add(std::move(callback)); }
 uint32_t Button::hash_base() { return 1495763804UL; }
 
+void Button::set_device_class(const std::string &device_class) { this->device_class_ = device_class; }
+std::string Button::get_device_class() {
+  if (this->device_class_.has_value())
+    return *this->device_class_;
+  return "";
+}
+
 }  // namespace button
 }  // namespace esphome