Allow over-riding api prefix as alternative way to get past github api limits

[tarasglek]

In my environment it would be far simpler to replace https://api.github.com/ with https://my-caching-proxy-that-injects-token.com. In CI most metadata apis will be hit repeatedly and should cache really well globally

Would you consider doing that via cmdline flag or env var?

Alternatively would be really nice to offer a list of api prefixes to try. Then I could get cloudflare to cache these for me via their public r2 buckets

[tarasglek]

There is also a small security matter of not sending GITHUB_TOKEN if using alternative api prefix