Make stepper interactive

[hdrury1]

Many users are trying to navigate the wizard with the stepper. We should make it possible to do so.

[chris-huggins]

@hdrury1 I suggest we use a solid blue do to show any "incomplete step that is further ahead than the current step" i.e. if the user is on a step but goes back, we show the last step in the state - this ensures they can get back there. Any step beyond the "incomplete step" would be shown in grey and would not be interactive.

e.g. user got to "editors" step and went back to the "details" step

Worth noting any step that can be skipped (i.e. is done) would have a tick so it would only be the furthest step that would appear in this state.

e.g. the user went further back to the files step - the details step is still "complete".

In the event that the user deletes information or causes a validation on the current step, the question is do we a) prevent them navigating away using the stepper? or b) show the stepper in an error state or use other validation?

I would argue we should scroll to the error if the user tries to navigate away with the stepper (as already planned when pressing "next"). This would be easier than any error states in the stepper

e.g. we should not rely on anything like this because of colour-blindness, and generally I think it requires too much thinking to take in

As a result, I think we need to be sure to work on this ticket first to get the "scroll to validation error" behaviour in first

#2071