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/RMakerQR.h

@@ -16,9 +16,9 @@ static void printQR(const char *name, const char *pop, const char *transport)
     snprintf(payload, sizeof(payload), "{\"ver\":\"%s\",\"name\":\"%s\"" \
                     ",\"pop\":\"%s\",\"transport\":\"%s\"}",
                     PROV_QR_VERSION, name, pop, transport);
-    log_i("Scan this QR code from the phone app for Provisioning.");
+    Serial.printf("Scan this QR code from the ESP RainMaker phone app.\n");
     qrcode_display(payload);
-    log_i("If QR code is not visible, copy paste the below URL in a browser.\n%s?data=%s", QRCODE_BASE_URL, payload);
+    Serial.printf("If QR code is not visible, copy paste the below URL in a browser.\n%s?data=%s\n", QRCODE_BASE_URL, payload);
 }
 
-#endif
+#endif