Release of SLES 15 SP7 BCI images into the registry as latest

[dirkmueller]

Following the announcement of SLES 15 SP7, the SLE BCI team is rolling over all containers and their latest tag to SP7 over the course of the next few days. In case you're using the :latest (or for language containers like golang, python etc any other floating tag) in your multi-stage build recipes, please be aware that you need to switch to 15.7 bci-base / bci-micro containers going forward to have a matching build environment in multistage builds.