Add secure mqtt example

examples/SecureMqtt/SecureMqtt.ino

@@ -0,0 +1,51 @@
+#include <CumulocityClient.h>
+#ifdef ESP8266
+    #include <ESP8266WiFi.h>
+#else //ESP32
+    #include <WiFiClientSecure.h>
+#endif
+
+const char *ssid = "........";
+const char *wifiPassword = "........";
+char *host = "xxx.cumulocity.com";
+char *username = "........";    // fixed credentials can be registered in the Administration section
+char *c8yPassword = "........"; // create a user in usermanagement with the "device"role and fill the credentials here
+char *tenant = "........";      //tenant ID can be found by clicking on your name in the top right corner of Cumulocity
+char *clientId = ".........";   //Should be a unique identifier for this device, e.g. IMEI, MAC address or SerialNumber
+const char *root_ca =
+    "-----BEGIN CERTIFICATE-----\n"
+    ".....CERT CONTENT............\n"
+    "-----END CERTIFICATE-----\n";
+
+WiFiClientSecure wifiClient;
+CumulocityClient c8yClient(wifiClient, clientId);
+
+void setup()
+{
+    Serial.begin(115200);
+
+    wifiClient.setCACert(root_ca);
+    WiFi.begin(ssid, wifiPassword);
+
+    Serial.print("Connecting to WiFi");
+    while (WiFi.status() != WL_CONNECTED)
+    {
+        delay(500);
+        Serial.print(".");
+    }
+    Serial.println("connected to wifi");
+
+    c8yClient.connect(host, 8883, tenant, username, c8yPassword);
+    c8yClient.registerDevice(clientId, "c8y_esp32");
+}
+
+void loop()
+{
+    delay(3000);
+    c8yClient.loop();
+
+    int8_t rssi = WiFi.RSSI();
+    char rssiStr[10];
+    sprintf(rssiStr, "%d", rssi);
+    c8yClient.createMeasurement("SignalStrength", "T", rssiStr, "*db");
+}