feat: add redirects to mfe for catalog-related legacy pages

[andrii-hantkovskyi]

This PR adds support for redirecting users from legacy catalog-related pages to their new Catalog MFE equivalents, based on the appropriate feature and waffle flag settings.

Key changes:

• Adds redirect logic to the legacy index, courses, and course_about views:
  • Home/index page redirects to MFE when ENABLE_CATALOG_MICROFRONTEND is enabled.
  • Courses listing page redirects to MFE whe ENABLE_CATALOG_MICROFRONTEND is enabled.
  • Course about page redirects to the Catalog MFE when ENABLE_CATALOG_MICROFRONTEND is enabled.
• Uses the newly added get_catalog_mfe_course_about_url helper for accurate about-page URL construction.
• Comprehensive tests are added for all redirection scenarios to ensure correct behavior for all flag combinations.

These changes allow for a controlled, flag-driven migration to the new Catalog MFE for all catalog-related user entry points.

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[peterkulko]

@andrii-hantkovskyi If this PR no longer depends on other waffle flags, do I need to update it + update the description?

[peterkulko]

Reopened at #37341