Imports: Explore whether it makes sense to move the Import handling out of the site-setup Stepper flow

[daledupreez]

Details

At present, our site migration Stepper flows allow users to pick between migrating their content and importing their content, and we direct users directly to /setup/site-setup/importList in cases where users have non-WordPress sites or choose to import content.

There are some subtle side-effects stemming from that, including complex behaviour about what it means to click on "Back" from that context, and issues when going forward in the flow and then clicking "Back" multiple times.

We should spend some time working out whether it makes sense to split these steps out into a dedicated Stepper flow where it may be easier to manage that behaviour and re-use the relevant steps from multiple starting points.

There is some discussion of this in #90710 (comment)

Checklist

• Explore pushing import steps to their own flow, and document findings
• Make a clear recommendation for moving forward

Related

#90710