RainMaker library: Minor changes (#5092)

- Use Serial.print instead of log_i for QR code helper information,
  so that it is always printed by default.
- Expose the RainMaker factory reset and wifi reset APIs.
- Simplify example to have only a Switch device. Create another example for custom device.
- Enable push button based Factory reset and Wi-Fi reset.
- Added support for the TimeZone service.
- Moved API doc to RainMaker library's top level README.
- Other minor doc changes.

libraries/RainMaker/src/RMaker.h

@@ -4,6 +4,7 @@
 #include "Arduino.h"
 #include "RMakerNode.h"
 #include "RMakerQR.h"
+#include "RMakerUtils.h"
 #include <esp_rmaker_standard_types.h>
 
 class RMakerClass
@@ -18,6 +19,7 @@ class RMakerClass
         esp_err_t deinitNode(Node node);
         esp_err_t setTimeZone(const char *tz = "Asia/Shanghai");
         esp_err_t enableSchedule();
+        esp_err_t enableTZService();
         esp_err_t enableOTA(ota_type_t type, const char *cert = ESP_RMAKER_OTA_DEFAULT_SERVER_CERT);
         esp_err_t start();
         esp_err_t stop();
@@ -25,4 +27,4 @@ class RMakerClass
 
 extern RMakerClass RMaker;
 
-#endif
+#endif