Hello! I am currently working on developing Dagster infrastructure, I believe we have very similar requirements.
Luckily, you don't need to create a single super-image. You can create several executor-images, and then set image per-job or per-op (you can also set images per-asset, please see my question above):
https://docs.dagster.io/deployment/guides/kubernetes/customizing-your-deployment
It's important, that your executor-images have to use you user-deployment image as a base. And you must not redefine CMD or ENTRYPOINTS. But you can install any dependencies that you need to run your code.
If you will have further questions - please contact me, I will try to help.
It's a pity, that this stuff is not documented, had to figure out a lot by myself.