Notify user when new image is available

[danielhollas]

In #184 we've changed the default behaviour so that the new AiiDAlab docker image is pulled only when user explicitly requests it. This is good for stability, but now users are not aware of updates. We should print a note when a new Docker image becomes available when the user tries to start a container.

[unkcpz]

This is a useful feature but not clear to me the definition of "new image".
It can be when there are new released versions (new tag) such as 2023.1012 -> 2023.1013. Or it can be using the latest tag and the latest tag is updated with the new image.
The second case is what #184 bought up.

[danielhollas]

Ah, indeed, I meant the second case. First case doesn't make much sense, since we can't know which new tags are available (at least not easily).

[unkcpz]

I did have a look at the link you shared https://hynek.me/articles/semver-will-not-save-you/ (Not very happy at beginning of the reading as well, but being persuaded a bit after) and come back to this issue, I am now understand the docker image release strategy of Jupyter docker stack that they running the released CI periodically. I didn't adopt this setting when I refactoring the CI workflow.
If it is also the case of our docker stacks, then when the tag is fixed the newly released image will be checked for all tags and it makes a lot sense to have this notification rather that just when using the image with tag latest.

[danielhollas]

then when the tag is fixed the newly released image will be checked for all tags and it makes a lot sense to have this notification rather that just when using the image with tag latest.

I am not sure what you mean here. But for a given profile, we now both the image and its tag, so we should hopefully be able to reuse the existing download logic to check if newer image is available when the user starts the container. No need to look at all tags.