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