Enable Storefront in Onboarding

[birkjernstrom]

Currently, in Onboarding we have a final step to integrate Polar. However, some might not want this vs. using the built-in storefront with Polar, and might not even know it's possible since we don't tell them about it.

So our goal is to merge these in a final task that takes more space: "Launch with Polar" offering either/or. Showcasing how to integrate Polar and next to it the ability to customize & launch a storefront.