Merge the miniforge-cuda repo into ci-imgs

[vyasr]

Currently we build a base image with CUDA and conda installed in the miniforge-cuda repo, then use that as a base for the conda images in the ci-imgs repo. Due to the tight coupling between these images, we trigger a rebuild of the ci-imgs whenever a PR is merged to miniforge-cuda. Given this tight coupling, I think we should consider merging these repos. Combining the repositories will make it easier to teach new build engineers about the pieces we have, and make it easier to maintain since it will reduce the amount of distinct processes required if there are changes that need to be coordinated between the repositories.