fix(element-template): copy versioned elementTemplate

[marstamm]

closes #631

[nikku]

I gave this PR a second thought: Given our future direction on "element template configured elements being first class citizens on the diagram" you could argue that replacing from service task to user task shall always unlink the template.

We'll otherwise end up in a situation where I cannot get rid of a template via replace anymore; in some contexts thought replace is the only thing we got (i.e. web-modeler).

So TLDR: If we introduce "retain template" as a feature here I'd rather keep "remove template during replace".

Does this make sense @marstamm @pinussilvestrus @MaxTru? Happy to provide further details on this.

[marstamm]

If we introduce "retain template" as a feature here I'd rather keep "remove template during replace"

Just to clarify: this is already existing behavior for element templates. We did not introduce something new here. It was just broken if the element had a version - therefore being inconsistent depending on which element template was applied.

I would propose to move the discussion if we want to change this behavior in a dedicated issue. In the current scope of Element Templates inside the properties panel, this behavior also makes sense as we have a dedicated unlink button for it.

[nikku]

Makes sense @marstamm. Will open that separate issue.

[nikku]

Follow up on #632 (review): #642

[nikku]

Works as intended.