Highlights banners on home page

[tom2drum]

Description and Related Issue(s)

Resolves #3157

This PR implements a highlights banners section on the home page that allows showcasing key Blockscout features and products. The feature supports displaying up to 3 banners at a time, with support for banner rotation and pinned banners that always remain visible.

Proposed Changes

• Added a new Highlights component that displays configurable banners on the home page
• Implemented banner rotation logic that prioritizes pinned banners and randomly shuffles others
• Added support for both internal page paths and external redirect URLs
• Created type definitions and validation schema for the highlights banner configuration
• Added tests for the Highlights component
• Updated environment variables documentation

Environment Variables:

• Added NEXT_PUBLIC_HOMEPAGE_HIGHLIGHTS_CONFIG to configure highlights banners via a JSON file URL. The config supports customizable banners with title, description, colors, backgrounds, side images, and link options. At least 2 banners are required in the config, with up to 3 visible at a time. Additional banners enable random rotation on page load.

Breaking or Incompatible Changes

None. This is a new feature that is opt-in via the environment variable.

Additional Information

The highlights section is only displayed on desktop viewports. On mobile, the section is hidden to maintain a clean layout. The banners support both light and dark color modes with separate styling options for each mode.

Checklist for PR author

• I have tested these changes locally.
• I added tests to cover any new functionality, following this guide
• Whenever I fix a bug, I include a regression test to ensure that the bug does not reappear silently.
• If I have added, changed, renamed, or removed an environment variable
  • I updated the list of environment variables in the documentation
  • I made the necessary changes to the validator script according to the guide
  • I added "ENVs" label to this pull request