Adding JSON to ROS Message Serialization Functionality

[ahmad-ra]

Enhancing the capabilities of ros_msg_parser by adding support for converting JSON strings into ROS messages without knowing the message type in compilation time. IMO, this functionality fills a crucial gap in the ROS ecosystem, particularly for scenarios where dynamic integration with external systems like MQTT brokers is required.

The motivation behind this update is to provide a dynamic integration mechanism similar to what is offered by the Python-based ros_bridge package, but for C++ which lacks reflection capabilities.

The core reason is to bridge ROS C++ with MQTT brokers using json payloads, dynamically casting json objects into ROS messages.

I edited mqtt_client and did pull request 51 , which depends on the updates of this package.

The mqtt_client already have a couple of open issues regarding this functionality.

Key Contributions:
-Implemented the functionality and added the required tests to ensure the correctness.
-Demonstrated the correct integration of the new function into the existing package by adding a test of the complete cycle of serialization, deserializeIntoJson, and serializeFromJson into a ROS message.
-Most importantly, I tried my best to integrate it seamlessly into the codebase following the same coding style, so that the edits don't look like a sore thumb!, and also insuring backward compatibility.

I believe this update benefits ROS interoperability, and is important to the community,