[5.x] Add success step

[Jade-GG]

This step seems to be necessary, as we ran into this issue on certain projects where the checkout success did not work. This may specifically only go wrong when using a payment provider, I'm not certain on the details.

[royduin]

A bit more details would be nice, will it play nice with the progress bar? Why didn't we need this earlier?

[royduin]

Let's wait for RAP-1908 so we can see possible visual differences

[royduin]

Could you update this PR and provide some more info?

[Jade-GG]

PR updated; the visual difference here is that it adds the success step to the list of steps at the top of the page during the checkout.

We currently have the success step added in the overwritten config in all v5 projects. While I don't remember exactly what went wrong, it had to do with not being able to find a success step after finishing payment and that caused it to throw you back into the cart instead of into the checkout success.