Build args in dockerfiles should not use realistic values

[jameslamb]

Description

Dockerfiles in this repo currently set realistic values as defaults for build arguments

dask-build-environment/dask/Dockerfile

Lines 1 to 3 in e121aa8

	ARG CUDA_VER=11.8.0
	ARG LINUX_VER=ubuntu20.04
	ARG PYTHON_VER=3.10

But never intentionally use those defaults... it's always expected that those build arguments will be fulfilled by values passed through to docker build:

dask-build-environment/ci/gpuci/run.sh

Line 64 in e121aa8

echo "docker build --pull -t ${BUILD_IMAGE}:${BUILD_TAG} ${BUILD_ARGS} ${BUILD_DIR}"

Those realistic values should be replaced with the literal string unset or similar.

Benefits of this work

Reduces the risk of silently building and tagging an image that's using the wrong configuration (because of mistakes in passing through build args).

Acceptance Criteria

• all configuration for build arguments is driver from outside of Dockerfiles

Approach

This: rapidsai/docker#689 (comment)

Notes

Created this issue based on #97 (comment)