Add nightly release

[jonatanklosko]

This makes several improvements to the release process, in particular Docker builds. The relevant changes are:

1. We now build the CUDA images on CI (thanks to Reduce CUDA images size #2724). Also, since installing CUDA directly is now straightforward, I removed the docker/ build scripts and custom base images, in favour of a single Dockerfile with VARIANT build argument.

2. Instead of building edge Docker images on every commit, we now build nightly images daily (or when explicitly triggered), this includes CUDA images. The workflow also dispatches Desktop builds, so Docker and Desktop nightly is aligned. I will remove the schedule trigger on Desktop CI right after merging this.

   For context, now that we build CUDA images on CI, it is very useful to have those available for changes on main. In particular, so that it is possible to run on main and properly use Fly runtime and Livebook Apps Docker deployments with CUDA images (also with changes from main). I don't think it's necessary to build all of these on every commit, especially that we can trigger the nightly release whenever needed.

3. Changing the base image of the default Docker image from Debian slim to Ubuntu. Those have basically the same size, and I don't think there's any particular reason for using Debian. This is mostly for consistency with the CUDA images, so that everything has the same base. For most purposes, Debian and Ubuntu are compatible (installing dependencies, etc), so this is a non-intrusive change, even if some users build on top of the Livebook image.

4. I removed the CUDA 11.8 image, so now we will only build -cuda12. Currently it still uses cuDNN 8, but I will bump it to cuDNN 9, as soon as we release new nx/xla using cuDNN 9.

[github-actions]

Uffizzi Preview deployment-55119 was deleted.

[josevalim]

we now build nightly images daily

🤨

[josevalim]

Beautiful work! 😍