Visual indicator for signed images

Story: As a user I want to visually identify image tags that have cosign signatures attached to them so that I can verify signing worked and view the actual signature string instead of the signature as an OCI artifact.

Acceptance criteria: 

• signed images have a visual indicator that is present when a corresponding cosign signature is found for the image in question via triangulation
• on hover the signature key is displayed
• when looking at the image details the signature OCI image location and the full signature key is displayed