--update flow result in not showing old version of images in report

[raDiesle]

Is your feature request related to a problem? Please describe.

Common use case:

• I want to compare images and if there is a diff to see the results, afterwards update old with new images by --update
• old version of images should be overidden at the same time to compare next time ( git versioned)
• when opening the report, I want to see the old and new images for comparison, but instead only the diff image and new image is shown, because old images had been overridden

Describe the solution you'd like

when using --update it should not just create diff images in report folder, but also copy the old images automatically for the ones with diff

Describe alternatives you've considered

a) call reg-cli twice, 1. to generate report 2. to only update
b) copy files manual after report is generated
c) call report without --update, then read report.json and copy diff old image files manual to override. also somehow tell report new location with new image locations

Additional context

Add any other context or screenshots about the feature request here.