Use cached index instead of GitHub API for recipe search

[homebysix]

Summary

This PR adjusts the behavior of autopkg search to leverage a locally cached index file instead of directly using GitHub's API to search for recipes. The index file is regenerated by GitHub Actions every 4 hours in this repo.

Details and test output coming soon.

Things to consider

• Merge new-search verb back into search if it performs well enough
• Add flag for accessing old search functionality (for troubleshooting or if index becomes unavailable)
• Build test cases
• Write feature announcement
• Update index repo to reflect production use

[homebysix]

Superseded by #910.