Add checksum to ci_job_artifacts

What does this MR do?

This simply stores sha256 checksum to ci_job_artifacts

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

/cc @ayufan @grzesiek

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/43599