Supply Chain Attestation generation error message

What does this MR do and why?

Related to Add SLSA Attestation Generation Error to CI bui... (#570341), this MR adds error messaging to the top of the build view page to communicate attestation generation errors to the user.

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Create an attestation with error in the rails console.

    project = Project.find_by_full_path('project-path')
    build = project.builds.last

    attestation = SupplyChain::Attestation.create!(
      project: build.project,
      build_id: build.id,
      status: 'error',
      predicate_kind: "provenance",
      predicate_type: "https://slsa.dev/provenance/v1",
      subject_digest: SecureRandom.hex(32),
    )

3. Go to /<path-to-project>/-/jobs/<build.id> to view the build page.
4. Verify that the "Attestation Generation Error" shows up on that page.
5. View any other build page, and verify that the "Attestation Generation Error" does not show on that page.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.