Task headers get lost when switching to User Task

[pihme]

Describe the Bug
If you add task headers to a Service Task/Send Task/Script Task and change the element to a User Task, the task headers are gone. This is inconsistent in comparison to e.g. changing a Service Task to a Send Task where the headers are kept

Steps to Reproduce

1. Create a Camnuda 8 BPMN diagram
2. Create a Service Task
3. Add headers to the service task
4. Use wrench menu to change Service Task to a Send Task
5. Notice that the task headers are copied over from the Service Task
6. Use wrench menu to change Send Task to a User Task
7. Notice that the headers were removed

Note that this only happens in this direction. If you add headers to a user task and then change it to a service task, then the headers are kept

Expected Behavior

Headers are kept

Environment

• Browser: Firefox
• OS: Ubuntu 21.04
• Library version: Desktop Modeler 5.0.0, current web modeler

[smbea]

I can confirm that the task headers are not maintained for user task. Moving to backlog

[smbea]

I couldn't figure out where this issue originates. Since it's not a priority, I will drop it for now and move it to back log.

[pinussilvestrus]

We missed adding bpmn:UserTask as allowed parent for the headers in the moddle descriptors.

I will add the missing piece.