#7423855 Add a progressbar to /marketplace/thank-you/

Proposed Changes

• When buying a marketplace plugin on a simple starter site, have the checkout “thank you” page render a progressbar to indicate the atomic transfer

New String (step 1):

Step 2:

Step 3:

What I have now looks like it needs some work:

Testing Instructions

• Have a simple site with starter plan

• Buy Xero

• Watch the thank you page

• Also try the page in other contexts (like sites that are already atomic)

Fixes #65314