Updated Gateway MQTT API

[samson0v]

PR description

The documentation updated for the Gateway MQTT API.

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[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
8 out of 11 committers have signed the CLA.

✅ RomenKost
✅ nickAS21
✅ ashvayka
✅ stitenko
✅ samson0v
✅ dashevchenko
✅ rusikv
✅ omahurin
❌ d2eight
❌ Andry925
❌ smykytenk0
_{You have signed the CLA already but the status is still pending? Let us recheck it.}