🐛 Fix Mi volume size parsing

🐛 Fix defaultStatusCode not overriding html return without default path

👷 Update GHA in consistency with other ppy repos

✨ Add mime type override for when always serving images

Our bucket for osu! avatars has inconsitent mime types (some avatars don't have an image mime type).
When enabled and mime type from S3 isn't image/*, overrides to image/jpeg.

✨ Add Prometheus metrics support

🔧 Adjust Kubernetes cache margin

We figured in production that 1G resulted in rare evictions. According to my measurements, 1G should be enough already and 2G way enough.
4G is kinda overkill but whatever at this point.

🐛 Increase safety margin to 1GB

nginx exceeded max_size by over 100M in production apparently

🐛 Increase safety margin to 1GB

nginx exceeded max_size by over 100M in production apparently

✨ Allow specifying custom keys zone size

✨ Allow specifying custom cache key