feat: implement ETag support for zip serving

What does this MR do?

Blocked by !527 (merged)
Blocked by !529 (merged)
Blocked by !634 (merged)
Blocked by !642 (merged)
Blocked by !645 (merged)

This MR includes the two MRs above as a PoC, once those are merged it's gonna need to be rebased.

Closes #82 (closed)

TODO

• I added the Changelog trailer (e.g. Changelog: feature) to the commits that need to be included in the changelog
• 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