Add ArduinoOTAClass::end() (#8379)

This adds the end() function for the ArduinoOTA class.

ESP32 has this implemented, however ESP8266 was lacking this.

libraries/ArduinoOTA/ArduinoOTA.h

@@ -62,6 +62,8 @@ class ArduinoOTAClass
     //Starts the ArduinoOTA service
     void begin(bool useMDNS = true);
 
+    //Ends the ArduinoOTA service
+    void end();
     //Call this in loop() to run the service. Also calls MDNS.update() when begin() or begin(true) is used.
     void handle();