Fix empty content-encoding for artifacts

What does this MR do?

Fix empty content-encoding for artifacts

When an artifact is returned without a content-encoding header from API, and pages running behind a reverse-proxy or k8s ingress - it may result in two content-encoding headers with the former one being blank and causing browsers to display garbage (because the latter is likely to be some compression).

Fixes #1167

TODO

• Feature flag
  • This feature does not require a feature flag
• I added the Changelog trailer to the commits that need to be included in the changelog (e.g. Changelog: added)
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines