Add support to see image tag build/push history

[lirantal]

Tell us about your request
I would like to be able to see all the history of an image tag's build and push to the repository so I can track whether an image tag has been built and pushed just once, or more.

Which service(s) is this request for?
Docker Hub

Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?
This helps understand whether image tags are actually specific and could be an acceptable replacement for image digests SHAs or do they get constantly rebuilt and pushed.

Are you currently working around the issue?
No way to find this information now.

[piroux]

Maybe a middle-step to this issue would be to have two different audit events in the repository audit log, so that it would be possible to differentiate between:

• a push creating a new image tag,
• a push overwriting an already existing image tag.

Right now, they both fall under "Tag Pushed" (repo.tag.push).

[tianon]

As an additional data point, I'll answer:

Are you currently working around the issue?

with: https://github.com/docker-library/repo-info 😬

(That repository serves other purposes too, but the number one most common reason I personally reach for it is to dig through the history of a tag or to search for a particular image digest or ID.)