[template] Use a user provided default constructor for TemplateButton (#19124)

esphome/components/template/button/template_button.h

@@ -6,6 +6,9 @@ namespace esphome::template_ {
 
 class TemplateButton final : public button::Button {
  public:
+  // User provided, not "= default": `new(p) TemplateButton()` would zero-fill .bss that is already zero.
+  TemplateButton() {}
+
   // Implements the abstract `press_action` but the `on_press` trigger already handles the press.
   void press_action() override{};
 };