[modbus_controller] Add on_command_sent trigger (#7078)

Co-authored-by: Leo Schelvis <leo.schelvis@gmail.com>

esphome/components/modbus_controller/automation.h

@@ -0,0 +1,19 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/core/automation.h"
+#include "esphome/components/modbus_controller/modbus_controller.h"
+
+namespace esphome {
+namespace modbus_controller {
+
+class ModbusCommandSentTrigger : public Trigger<int, int> {
+ public:
+  ModbusCommandSentTrigger(ModbusController *a_modbuscontroller) {
+    a_modbuscontroller->add_on_command_sent_callback(
+        [this](int function_code, int address) { this->trigger(function_code, address); });
+  }
+};
+
+}  // namespace modbus_controller
+}  // namespace esphome