Use template for rapids stable and nightly version in docs

[ncclementi]

Across the docs we have instances where we need need to specify rapids versions and those will change depending on if they are stable or nightly, but they will also change every time there is a release.

For example in a case like

conda create -n rapids-26.04 -c rapidsai-nightly -c conda-forge rapids=26.04 python=3.13 'cuda-version>=13.0,<=13.1.1'

In the deployment repo we do it via:

https://github.com/rapidsai/deployment/blob/4bc97baef108058700218ee173019de9f3c10d87/source/conf.py#L25-L70

https://github.com/rapidsai/deployment/blob/main/extensions/rapids_version_templating.py

Maybe something similar could help here