Conda config option to specify CONDA_SUBDIR environment variable

New feature

Usage scenario

I am running Nextflow on an M1 Mac. The version of Conda I have installed (mambaforge arm64) allows for the creation of both osx-64 and osx-arm64 environments seperately, either by calling:

CONDA_SUBDIR=osx-64 conda create -n someenv ...
conda activate
conda config --env --set subdir osx-64

or by setting:

conda create -n someenv
conda activate someenv
conda config --env --set subdir osx-64
conda install ...

As bioconda currently only releases builds for osx-64, this allows for the installation and running of x64 environments on an ARM CPU, running through the Rosetta translation software, allowing tools without native versions to be run. It would be great if there was some kind of process directive to specify this when creating an environment - otherwise, the only workaround is to create the environment locally and specify the path to it in the conda directive, which is not as portable.

Suggest implementation

Either a process directive conda.subdir which can specify this directly, or alternatively a more general process directive which allows conda config --env --set ... to be run and set many environment specific config settings (although having looked at the list, I am not sure what other options would be desireable to set).