Deploy workflow with parallel multi-instance service task

[saig0]

Is your feature request related to a problem? Please describe.
I want to use parallel multi-instance on a service task to execute it for each element of a collection.

Describe the solution you'd like

• I can mark a service task with the multi-instance marker and isSequential=false (default)
• I can define the collection variable to iterate over it
• I can define the variable name to store the element of the instance in
• when the service task is entered, it creates one instance of each element in the collection
• when all instances are completed, the service task is left

Describe alternatives you've considered

• model a loop in the BPMN using gateways -> hard to understand
• control the execution externally -> workflow is not self-contained

Additional context

The BPMN XML could look like:

    <bpmn:task id="Task_1f0s1iu" name="task">
      <bpmn:multiInstanceLoopCharacteristics 
        zeebe:inputCollection="items" 
        zeebe:inputElementVariable="item" />
    </bpmn:task>

[saig0]

Following our current Zeebe model approach, it would look like:

    <serviceTask id="task" name="task">
      <extensionElements>
        <zeebe:taskDefinition type="test"/>
      </extensionElements>
      <incoming>...</incoming>
      <outgoing>...</outgoing>
      <multiInstanceLoopCharacteristics id="...">
        <extensionElements>
          <zeebe:loopCharacteristics inputCollection="items" inputElement="item"/>
        </extensionElements>
      </multiInstanceLoopCharacteristics>
    </serviceTask>