Topic information added

[DarshanDodal]

Change Summary:
Refactored the _onMessage method in the codebase to improve the accessibility of topic information for messages received. The primary modification involves updating the way messages are processed and observed, ensuring that the topic is explicitly included in the data passed to observers.

Details:
Replaced the original direct usage of parsedMessage in the observer callback with a structured object containing both the topic and msg properties.
Introduced a small adjustment to the parsing of the incoming message (msg) to ensure that the resulting parsedMessage is a valid PubSubContent object.
For enhanced access to the topic information, added the topic as a property to the parsed message using the topicSymbol property.

Reasoning:
Improved the structure of the message passed to observers to explicitly include the topic information.
Ensured proper parsing of incoming messages to prevent potential issues with invalid JSON.
Facilitated easier access to the topic on which the message is received, enhancing the overall usability of the Pub/Sub mechanism.

Impact:
This change impacts the way messages are handled by observers subscribed to specific topics. The modification ensures a more consistent and structured format for the data passed to observers while providing convenient access to the associated topic.

Additional Notes:
The adjustment is made with the specific goal of enhancing access to topic information, contributing to improved code readability, maintainability, and usability of the Pub/Sub functionality.
By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.