MD5 and SHA1 checksum header for Artifactory

[skycaptain]

This is a follow-up on #752. Artifactory seem to require the SHA256 checksum from the client along with MD5 and SHA1 checksums in the request header. Without all three checksums, Artifactory reports insufficient client checksums. As shown in the screenshot, while the SHA256 is marked as (Uploaded: Identical), the other checksums are marked as (Uploaded: None):

Several possible solutions come to my mind:

• Allow adding multiple checksum_header
• Hard-code these headers directly in internal/pipe/artifactory, since they're always needed for Artifactory.
• Use Jfrog’s official Go library, which automatically handles the right headers: https://github.com/jfrog/jfrog-client-go
• Add a checksum function to the template function map, allow adding the checksums via custom_headers e.g.:

artifactories:
  - name: production
    target: http://<Your-Instance>:8081/artifactory/example-repo-local/{{ .ProjectName }}/{{ .Version }}/
    custom_headers:
      X-Checksum-MD5: "{{ md5 .ArtifactPath }}"
      X-Checksum-SHA1: "{{ sha1 .ArtifactPath }}"
      X-Checksum-SHA256: "{{ sha256 .ArtifactPath }}"

I prefer the last option as it's the simplest to implement without breaking existing features. Adding hashing functions to templates would also enable their use elsewhere—for example, uploading files to object storage using paths like https://artifacts.example.com/{{ sha256 .ArtifactPath }}/.

EDIT: Applied suggestion from #5743 (comment).

Original suggestion

artifactories:
  - name: production
    target: http://<Your-Instance>:8081/artifactory/example-repo-local/{{ .ProjectName }}/{{ .Version }}/
    custom_headers:
      X-Checksum-MD5: "{{ checksum .ArtifactPath \"md5\" }}"
      X-Checksum-SHA1: "{{ checksum .ArtifactPath \"sha1\" }}"
      X-Checksum-SHA256: "{{ checksum .ArtifactPath \"sha256\" }}"

[skycaptain]

Implemented by #5743.

[caarlos0]

thanks