Add NodeListener and Increase Code Coverage

[ShrutiC-git]

In this PR, the following changes have been made:

1. Add NodeListener to represent node-online and node-offline kind of event.
2. Add more event-data relevant to the event which is being emitted.
3. Add code coverage and tests for existing functionality.
4. Update README to have event metadata and data info

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• [X] Ensure that the pull request title represents the desired changelog entry
• [X] Please describe what you did
• [ ] Link to relevant issues in GitHub or Jira
• [ ] Link to relevant pull requests, esp. upstream and downstream changes
• [X] Ensure you have provided tests - that demonstrates feature works or fixes the issue

[ShrutiC-git]

Failure merging.