durable attributes: image-level attributes need to be durable

[rchincha]

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

In UI, it is useful to show image-level attributes such as "how many times downloaded", "CVEs affected", etc

Note that we cannot store these in manifest annotations since it could affect image signatures.

Describe the solution you'd like

Store these in a separate db. We have one for other things anyways.

Describe alternatives you've considered A clear and concise description of any alternative solutions or features you've considered.

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

[andaaron]

Let's cover the user level attributes as part of https://github.com/project-zot/zot/issues/592

[andaaron]

In review: https://github.com/project-zot/zot/pull/979/commits