Message start event templates should not have a Correlation key (process) property

[chillleader]

Describe the Bug

All generated message start event element templates have both Correlation key (process) and Correlation key (payload). However, Correlation key (process) does not apply to message start event (since the process is not yet running and has no variables). Although present in the element template, this redundant property doesn't show up in the latest versions of the Modeler.

Steps to Reproduce

1. Go to the Modeler
2. Apply a message start event element template for any connector
3. Make sure there is no Correlation key (process) in the properties panel
4. Inspect the element template JSON and discover the Correlation key (process) property there

Expected Behavior

We should remove this property from all message start event templates

[chillleader]

Concern: correlation key is needed for message start events inside subprocesses

[johnBgood]

Discussion about the example below (https://camunda.slack.com/archives/C02JLRNQQ05/p1725454462715789)

Example BPNM:

simpleTest.bpmn.txt

[nikku]

We identified that correlationKey cannot simply be removed, but there is different use-cases for message start events:

• Inside an event sub-process a correlationKey can be defined to tie the message subscription to the parent process instance
• On the root scope correlationKey must not be defined.

The documentation currently states:

The binding name of correlationKey is not applicable to message start events on a process. In such cases, the property is automatically hidden.

So while this property is redundant in some scenarios, it is applicable in others, and our implementation should already handle that case (*).

* To be verified 🙂