Use base image SHA instead of tag

[squakez]

We're actually using a tag to start the image building process. It would be convenient to get the SHA of the image in order to have a fully reproducible build.

[github-actions[bot]]

This issue has been automatically marked as stale due to 90 days of inactivity. It will be closed if no further activity occurs within 15 days. If you think that’s incorrect or the issue should never stale, please simply write any comment. Thanks for your contributions!

[michalvavrik]

I'd like to give it try and implement this. I may need some pointers as I am not quite sure where to start. I'll figure this week if all is clear or I have concrete questions regarding the issue description.

[squakez]

Great! Feel free to ask. As an hint, you can notice a warning during the building process in Jib as we use an image with a tag. I think we should try to figure it out how to convert that into a reproducible build instead.