[Feature Request] add API endpoint to browse given build artifact

Description

from the REST API currently we can only retrieve the artifacts.zip, could be useful to have a way to browse the content of the artifact and access directly single files, just like the main UI

Proposal

• list content of the artifact
  GET /projects/:id/builds/:build_id/artifacts/browse
• access single files
  GET /projects/:id/builds/:build_id/artifacts/browse/afolder/afile.xyz