[WIP] Updated MQTT connector docs

[samson0v]

PR description

The documentation updated for MQTT connector.

Link checker

The links will be checked by the build agent automatically once you create or update your PR.

You can use the following command to check the broken links locally.

docker run --rm -it --network=host --name=linkchecker ghcr.io/linkchecker/linkchecker --check-extern --no-warnings http://0.0.0.0:4000/

[CLAassistant]

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