feat: Indigo updates for the Course Catalog MFE

[arbirali]

Description

This PR introduces key enhancements to the Course Catalog MFE as part of the Indigo theme integration in the Tutor-Indigo plugin.

The update includes the addition of plugin slots in the course card, enabling greater extensibility and customization, along with a new course card component adapted to work seamlessly with Indigo’s design system.

These changes improve flexibility for operators to inject custom UI elements into course cards and ensure styling consistency with the Indigo theme across the catalog experience.

Key Changes

• Added course card plugin slots to enable customization points within the Course Catalog MFE.
• Introduced a new Course Card component that:
  • Adheres to Indigo theme styles and tokens.
  • Serves as a central reusable component for course listings.
  • Provides structured places for plugin injection via slots.
• Ensured that the new course card component works consistently with the existing MFE layout and interaction patterns.
• Verified integration with the Indigo theme variables for color, typography, spacing, and responsiveness.

Before	After

[Faraz32123]

Once brand PR is merged, then after updating a brand version in plugin.py, we can merge this PR.

[arbirali]

@Faraz32123 Tag is updated to indigo-3.1.0 from indigo-3.0.0 now