Consider using "plugins" for workers distribution

[worried-networking]

Is your feature request related to a problem? Please describe. At the moment, all the workers are expected to be distributed within bt-mqtt-gateway itself. It could lead to some issues:

• Not really straightforward dependencies handling
• All the workers expected to have the same license
• "Single point of failure" in terms of distribution — we're relying on @zewelor's availability always to be able to merge new workers and maintain the issues/code quality for all of them

Describe the solution you'd like I propose using the way described in the Python docs: https://packaging.python.org/guides/creating-and-discovering-plugins/, especially the option titled "Using package metadata". This method fully covers my concerns.

Describe alternatives you've considered None, to be honest, I'm open to ideas.

[worried-networking]

You can find an example of entry-point-based plugins system in https://github.com/philipov/python-plugins-demo