Java/iot3core: send messages to telemetry service for MQTT exchanges

[mathieu1fb]

Features;

IoT3 Core SDK: Telemetry is now operational when publishing and receiving MQTT messages, using the OpenTelemetry client: service_name, span.status, span.name, span.kind, attributes and links are all set according to the specification (see #128).

Closes: #128

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How to test

1. Clone the its-client project on your IDE.
2. Ensure that you have Gradle to be able to build the java/iot3 modules (core, mobility and examples).
3. Find the Iot3CoreExample class in the examples module, and set appropriate values for the following fields:

   // MQTT parameters
   private static final String EXAMPLE_MQTT_HOST = "mqtt_host";
   private static final int EXAMPLE_MQTT_PORT_TCP = 1883;
   private static final int EXAMPLE_MQTT_PORT_TLS = 8883;
   private static final String EXAMPLE_MQTT_USERNAME = "mqtt_username";
   private static final String EXAMPLE_MQTT_PASSWORD = "mqtt_password";
   private static final String EXAMPLE_MQTT_CLIENT_ID = "mqtt_client_id";
   // OpenTelemetry parameters
   private static final String EXAMPLE_OTL_HOST = "telemetry_host";
   private static final int EXAMPLE_OTL_PORT = 4318;
   private static final String EXAMPLE_OTL_ENDPOINT = "/telemetry/endpoint";
   private static final String EXAMPLE_OTL_USERNAME = "telemetry_username";
   private static final String EXAMPLE_OTL_PASSWORD = "telemetry_password";

4. Run Iot3CoreExample.

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Expected results:

1. On the console, you should see 3 messages being published at 2 seconds interval, on 3 different topics: The first and third messages should be received back, while the second should not be.
2. In Jaeger, you should be able to find the logs of the 3 published messages, and of the 2 received messages with links to the respective published ones.