Add plugin loading system to workit

[OlivierAlbertini]

🚀 Feature Proposal

Add plugin loading system to workit in order to load tasks with common interfaces

Motivation

By using workit over multiple projets, we saw that we have many repo that contains the same code (configuring workit among other stuffs)
and those repos need to maintain the same dependencies. Besides, a lot of workers pulls Camunda and sometime it's not necessary to have a dedicated worker.
When we work with multiple projets and each projet has a team, each team should be responsible to develop the bpmn related to the project as well as the tasks. bpmn and tasks should be bundled through a plugin that is loaded inside the worker.

For those reasons, we would like to add the possibility to load tasks through a plugin system. In this way, we can have one worker and multiple librairies that contains tasks for each project / bpmn depending the way you want to decouple librairies.

With this feature we have the flexibility to load all libraries in the same worker or we can dedicate a worker for some librairies.