Applying or upgrading element template with `entriesVisible=true` overrides non-templated fields

[nikku]

Describe the bug

As a user I want to only template a particular subset of properties, i.e. want to template a zeebe:property to inject additional meta-data into an object. I use entriesVisible=true with my element template, and maintain other stock Camunda properties along with the special property:

As I use entriesVisible=true I assume that I can use non-templated properties, and that these are kept during template assignment and upgrade. What happens instead is that these properties are removed, albeit still visible ("valid") after the change:

Steps to reproduce

1. Configure service task with job type or any other Camunda property
2. Apply element template
3. (Alternatively, upgrade from an applied template)
4. See that template properties (a simple zeebe:property binding) is established, but other entries are lost

Expected behavior

Templates that configure entriesVisible=true are special and we want to keep whatever is not templated, when the template is applied, or upgrade.

Environment

• OS: Any
• Camunda Modeler Version: v5.29.0
• Execution Platform: Camunda 8
• Installed plug-ins: None

Additional context

Related to SUPPORT-24211