[incubator-kie-issues#1326] `string join` function with `list` parameter in string format invocation is missing

[yesamer]

The function string join (list <string>, delimiter <string>) is missing.

Example string join("a", ".")

This is not present in the specs, but there are a couple of TCK tests that require it, probably to manage the case of a single-item list.

Honestly, I don't see the need to manage such a case (i.e. a string join("a", ".") will produce "a") - Adding it just to fix the TCK tests.

Could make sense to discuss in TCK if that function is required? @gitgabrio @baldimir

@baldimir Provided the original fix.

[yesamer]

Ok, let's put this on hold and raise the point at the TCK meeting

[yesamer]

Closing, it will be managed in a separate PR.