Explore a custom executor

[maleadt]

We could use the podman one, which is supposed to be a drop-in replacement for Docker: https://github.com/jonasbb/podman-gitlab-runner

Using custom executors can have quite some advantages:

• select a suitable GPU (with --gpus instead of the runtime hack) based on tags (multigpu, big-gpu, recent-gpu), memory usage, or other policies (entire gpu for a job, for example)
• cache artifacts without zipping (currently accounting for significant run time)
• set JULIA_NUM_THREADS per-runner
• etc

[christopher-dG]

GitLab docs on custom executors