Added support for MQTT notification mechanism

[pooja1pathak]

Proposed changes

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

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[github-actions]

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[c0c0n3]

@pooja1pathak great work so far, but I'd be even better if we could keep the code a bit cleaner. So I've suggested some minor refactorings...thanks alot!!!

[c0c0n3]

@pooja1pathak excellent refactoring, thank you a stack!
should we add some tests?

[pooja1pathak]

@c0c0n3 I am not sure about the test cases for this PR. If you have something in mind, then I can work to that.

[c0c0n3]

@pooja1pathak maybe you could put together a docker compose file w/ orion (a version that supports mqtt), quantum leap, plus mongo, as a backend for orion, and crate as a backend for quantum leap. Then write a pytest fixture to set up an mqtt sub for quantum leap so that orion can send data to quantum leap over mqtt. Having that in place, you could write simple tests to send an entity to orion and then check the entity data ends up in crate.