Support intermediate message catch event templates

[barmac]

What should we do?

In order to accomplish camunda/camunda-modeler#3403, we need to implement proper support in the element templates infrastructure:

• Create event with message event definition from template
• Replace already existing event definition when template is applied
• Support bpmn:Message bindings:
  • property
  • zeebe:subscription
  • as unconditional properties
  • with conditions
• Generate unique message name via generatedValue: 'uuid'
  • apply template
  • create from template
• Hide templated message from messages list
• When template is removed, remove message altogether
• Apply should create a new message instead of reusing the referenced one
• Copy and paste in the same diagram should create a new message
• Replace with standard should remove the message
• Handle template change (old and new template specified)
• Remove message when element is removed
• Message select should stay on top of the group
• (optional) Modeling#updateModdleProperties does not add label for events name modification bpmn-js#1872

Why should we do it?

Related to camunda/camunda-modeler#3403

[barmac]

In the current state, we don't set $parent on message. I will look into this in spare time.

[barmac]

I will implement a fix for bpmn-io/bpmn-js#1872 as this is an annoying blocker for external label elements.

[barmac]

I implemented unlink and removal. At the moment, copy and paste does not work properly as we reuse the message unintentionally. I should build a prototype for this tomorrow.

[barmac]

What is still missing is "Remove message when the shape is removed" 🤡

[barmac]

Follow-up:

• Unlink should not remove message from the diagram but only remove the zeebe:modelerTemplate property #914
• Message should be removed if no message properties exist on template #915

I did not create an issue for magic string as it's a refactoring.