feat: support zeebe:TaskListener

[misiekhardcore]

This adds support for zeebe:TaskListener contained in zeebe:TaskListeners container.

related to camunda/camunda-modeler#4590

[barmac]

Please have a look closely at the XML example from camunda/camunda-modeler#4590 (comment)
We need the element names to exactly match the XML so that the engine can understand it. Note that this project (zeebe-bpmn-moddle) is only used on the frontend while the engine parses BPMN with its own BPMN model.

   <zeebe:taskListeners>
     <zeebe:taskListener eventType="create" type="create_listener" retries="2"/>
     <zeebe:taskListener eventType="assignment" type="assignment_listener"/>
     <zeebe:taskListener eventType="update" type="update_listener" retries="8"/>
     <zeebe:taskListener eventType="complete" type="complete_listener"/>
   </zeebe:taskListeners>

[misiekhardcore]

@barmac I see 👍🏽 I was mislead by the issue name and blindly followed User task listener

[barmac]

A few last steps before we merge this.

[barmac]

Let's make this match the expectations. We want the task listeners to be allowed in bpmn:userTask only.

[barmac]

BTW how come the test is passing if we read a task here and check for user task as the type?

[misiekhardcore]

it passes for bpmn:userTask and bpmn:task but does not for bpmn:endEvent for example 🤔

[barmac]

Feel free to merge this PR once you're done.