Enable an optional string identifier property so callback can properly identify a step

[justin-hackin]

I have a tour that visits a particular element more than once. I need to perform an action upon reaching this element the first time, thus I can't use the target property of the step for identification. Elsewhere it has been suggested to use the title property for identification but I don't want a title on my step. I could use the index of the step but then the application would break if I added a step at the top of the list. Thus, I'm proposing this library enable an optional string property id in the typescript definitions for Step. Do you think there a better solution to the problem though? If not, and this proposal is approved, I could put in a quick PR

[gilbarbara]

hey @justin-hackin

You could filter your steps by the target selector and match the tour index with the first occurrence of the filtered steps.

[justin-hackin]

That still suffers from the brittleness I spoke of with index targeting, though less. I just extended the Step definition myself and it works fine.