Remove the ability to model collapsed sub-processes

[nikku]

Is your feature request related to a problem? Please describe.

Collapsed sub-processes are not well supported across the Camunda tool stack (Cockpit, Optimize, ...). Generally, users should resort to call activities to break up their big processes.

Describe the solution you'd like

In order to not cause users trouble when automating their processes we should disallow the usage of collapsed sub-processes. To support it we'll do the following:

• [x] Create and publish bpmn-js plug-in:
  • [x] Replace Sub Process (expanded) and Sub Process (collapsed) with Sub Process and Expand (not reversible)
  • [x] Allow to turn tasks into collapsed Sub Process
  • [x] Disallow to collapse Sub Process
• [x] Disable collapsing of Sub-Processes in Camunda Modeler

Describe alternatives you've considered

• [x] We could simply discourage the usage of collapsed sub-processes via a lint rule (cf. https://github.com/camunda/bpmnlint-plugin-camunda/pull/1)

Additional context

Cf. sub-call.bpmn

Related: https://app.camunda.com/jira/browse/SUPPORT-6256?focusedCommentId=118488&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-118488

[barmac]

Foundations in diagram-js for the plugin are already merged. Now we need a bpmn-js release in order to integrate the plugin with Camunda Modeler.