new function get_build_artifact_as_bytes to replace get_build_artifact (incompatible with artifacts not json-formatted)
+ use a stream to download binary artifacts
all artifacts are returned as bytes to avoid encoding issues
and an exception NotFoundException is raised in case of missing artifact
Closes-Bug: #1973243
Change-Id: I24ce4ecd854f8a19ed4d760404adb7d1ac6b5509