refactor CUDA versions in dependencies.yaml

[jameslamb]

Description

Contributes to rapidsai/build-planning#7.

Proposes splitting the cuda-version dependency in dependencies.yaml out to its own thing, separate from the bits of the CUDA Toolkit this project needs.

Benefits of this change

• prevents accidental inclusion of multiple cuda-version version in environments
• reduces update effort (via enabling more use of globs like "12.*")
• improves the chance that errors like "conda recipe is missing a dependency" are caught in CI

[pentschev]

/merge