We should have a publish scripts for the testing images we need, and we should not depend on third party images

### Description

See #3479 for the last straw.

Our tests do depend on a number of images that we do not control - usually on Docker Hub.
There are good reasons to test Docker Hub - just not to use third party images.

Also, even for the images that do not change (hosted on ghcr.io), we do not have a way to repush them if we needed to.

Suggesting we create a nerdctl account on hub, and start pushing the images we need there.

@AkihiroSuda I can take care of this, but then I would need to transfer the account to you.
Or you take care of it directly instead.

Then I can come up with a script that would push everything we need and we get rid of the dependencies on `busybox` (etc.).

LMK.

### Steps to reproduce the issue

na

### Describe the results you received and expected

na

### What version of nerdctl are you using?

na

### Are you using a variant of nerdctl? (e.g., Rancher Desktop)

None

### Host information

_No response_