Add the ability to pull files from Release links

[haboustak]

Add "release-link" as an artifact source. For links to ZIP files, support installing individual files within the artifact.

Install the release link file

- project: gitlab-org/cli
  ref: v1.65.0
  source: release-link
  install:
      glab_1.65.0_windows_amd64.zip: artifacts/amd64/windows/glab_1.65.0.zip

Install a single file from the release link

- project: gitlab-org/cli
  ref: v1.65.0
  source: release-link
  install:
      glab_1.65.0_windows_amd64.zip/bin/glab.exe: artifacts/amd64/windows/glab.exe

[haboustak]

There is no requirement that the URL for a release link points to GitLab. These links can point to unauthenticated resources on the Internet (third-party file hosting services, CDN, etc.). When downloading a release link, art would need to prevent sending the GitLab auth token to the destination server.

In addition, a job token can only access certain API endpoint Urls, which are unlikely to be used for release links.

For the first round, Generic Packages (#52) seems like a more appropriate solution for downloading tagged build products outside of CI job artifacts.