Support `S3_Prefix` for S3 external storage

[maxswjeon]

Hi, I appriciate your work. I found out that each services (assets, recordings, sourcemaps) requires each buckets. However, we are in a special situation where we can use only one S3 bucket. We would really appriciate if we can support prefixed storage on each services.

Change Summary

Current

Each services (assets, recordings, sourcemaps) uses each buckets

To-be

Each services can use one bucket with different prefixes