Add mqtt service

[NeoCortex97]

Description

I would like to add mqtt subscriber and mqtt publischer services, since it would grant huge flexibility for connecting to iot devices.

[NeoCortex97]

This maybe could enable support to tie into systems like node-red, home assistant, or other smart home systems to support various features that Lumiastream offers.

[Nils-witt]

Support for MQTT was added in PR #265

[hlxid]

@Nils-witt this Issue will be closed once the documentation has been updated to include a entry for your mqtt sample bundle.
It would be nice if you could do it, because you already have created the bundle and know your service best, but you don't have to.