build + build_and_deploy strategy to test individual commits
As discussed today, huge artifacts create problems in GitLab CI. To come up with a CI that also checks whether individual commits do build, I did this
https://gitlab.hrz.tu-chemnitz.de/dcgc-bfx/singularity-test/-/blob/main/.gitlab-ci.yml
So, instead of having a build and a deploy stage, there now are a build and a build_and_deploy stages/jobs and both are mutually exclusive.