Download a single artifact file by job ID

[Nowaker]

Feature request: https://docs.gitlab.com/ee/api/job_artifacts.html#download-a-single-artifact-file-by-job-id

Currently, the library allows to download all artifacts in gzip format only.

[Nowaker]

Here's how I achieved it myself:

  project_id = Gitlab.client.url_encode(project)
  json = Gitlab.client.get(
    "/projects/#{project_id}/jobs/#{artifact_job.id}/artifacts/operation.json",
  ).to_h.to_json

A minor inconvenience was the fact .get returned the objectified hash thing, whereas I'd prefer a blob. I didn't know how to achieve that.