Implement a way to make static images for analyses

With the removal of support for CentOS7 it has been revealed that the build system is prone to issues due to certain images being marked as obsolete by CERN. This lack of support translates into problems in the build system, unavailable repositories, etc. Since we need to maintain the images for analysis preservation, we must come with a way of placing these images in a static location, preferably in Docker Hub. However, there is no lhcb account there, so it might be beneficial to ask to create one. We do not plan to use the GitLab container registry because this can be cleared during updates, leading to data loss.