Import from Course stepper UI

[bradenmacdonald]

https://www.figma.com/design/4wsTUbieYphB2qchIPxm10/%E2%9C%8F%EF%B8%8F-Library---Course-Authoring-v1.0--Open-edX-?node-id=14258-39021&t=6doa6ywVTLoi4sBK-4

• Add the "+ Import Course" button to Import Home Page #2523 , behind a feature flag / env variable for now.
• Clicking it opens a modal with the stepper UI
• Step 1: Select Course
  • Note that we need to display a badge on courses that were previously imported.
• Step 2: Analyze UI
  • Create the loading state only (screenshot below)