Merge pull request #6 from ppy/preserve-upstream-cache-control

✨ Preserve upstream Cache-Control headers

🐛 Fix Mi volume size parsing

🐛 Fix defaultStatusCode not overriding html return without default path

👷 Update GHA in consistency with other ppy repos

✨ Add support for entrypoint scripts

✨ Allow overriding system DNS resolvers

✨ Allow overriding default (404) status code

✨ Add mime type override for when always serving images

🐛 Fix purge when overriding default cache path

✨ Add Prometheus metrics support

🔧 Adjust Kubernetes cache margin

🐛 Increase safety margin to 1GB

✨ Allow specifying custom keys zone size

✨ Allow specifying custom cache key