Allow to access traces on Object Storage

Once we make traces to be artifacts, we can migrate them to Object Storage. However, this requires them to be accessible by GitLab application in efficient way.

This issue is to track all the work related to this.

One way to achieve that is to use Content-Range requests to Object Storage to read only chunks of data to minimise the amount of transfer between OS and GitLab.

The PoC implementation of chunked reader compatible with Gitlab::Ci::Trace::Stream can be found here: gitlab.com/snippets/1685610