[FEATURE] expose metric for current image creation timestamp & current image available

[ctrought]

Is your feature request related to a problem? Please describe.
Having the image creation timestamp as a metric would be useful and help to discover images in use that are old/abandoned, that may already be at the latest. For example, an image already at latest that was created X months/years ago - can be flagged as a potential abandoned/image that needs investigation or a new version to be built.

The second part of this is it would double as a way to know if the current image no longer exists on the repo which would be useful to avoid potential image pull errors in the future. I could see that either being implemented as separate metric (version_checker_current_is_available), or by setting the proposed image creation timestamp metric to an invalid value, like null/0 and use that as a way to detect whether the image is not available on the remote repo. #319 is somewhat related (registry accessible)

Describe the solution you'd like
Expose the current versions creation timestamp (queried from remote reg)

Describe alternatives you've considered
Trying to find another tool to handle this.

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