GitHub Metrics utility: Add sample app repos

[dacharyc]

This PR includes some updates to the GitHub metrics utility we run bi-weekly:

• A small refactor to store the repo details in a JSON file we read at runtime, instead of hard-coding them in the index.js file. This is similar to the pattern we're using in github-check-releases
• Add the sample app repos to the list of repos we're fetching metrics for
• Remove an unused import in one of the files
• Bump dependency versions to current versions for the get-metrics utility

[cbullinger]

🚀