Added support for MQTT notification mechanism

[pooja1pathak]

Proposed changes

A way to store data from mqtt queues. Fix for issue #609

Types of changes

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• [ ] Bugfix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Maintenance (update of libraries or other dependences)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• [x] I have read the CONTRIBUTING doc
• [x] I have signed the CLA
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] I have run all the existing tests locally (not just those related to my feature) and there are no errors
• [x] After the last push to the PR branch, I have run the lint script locally and there are no changes to the code base
• [x] I have updated the RELEASE NOTES
• [x] I have added necessary documentation (if appropriate)
• [x] Any dependent changes have been merged and published in downstream modules

Further comments

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