Handle multiple package cache and envs dirs

[adriendelsalle]

Description

libmamba currently only consider root_prefix for packages cache and envs/ directory when using a named environment. We should be able to support multiple cache and env dirs, and make them configurable from rc files using pkg_dirs and envs_dirs.

The notion of root_prefix maybe also has to be modified in multiple places to be sure the root_prefix is a read-only source. I think about some places like: https://github.com/mamba-org/mamba/blob/ceb85460fd22f6cb2e7446622b655dff7036718a/src/core/channel.cpp#L62

[adriendelsalle]

I still didn't have implemented multiple envs dirs, only multiple caches

[yarnabrina]

@adriendelsalle, @wolfv

Is there any plan to support envs_dirs in the configuration file for micromamba? Details of the issues are available in #1999. Personally I'm not much interested in multiple directories, but having control over the location is required for our particular use case of managing backup of Kubeflow notebooks.

[dhirschfeld]

I've ended up here after discovering that micromamba appeared to be ignoring my envs_dirs config.

I just have one env dir, but I'd like to be able to change it from the default of $ROOT_PROFIX/envs

[adriendelsalle]

sorry for the late reply, looks like envs_dirs config is set after env_name:

trace    libmamba Compute configurable 'env_name'
trace    libmamba Compute configurable 'envs_dirs'

a dependency should be added

the hook also looks like incorrect: https://github.com/mamba-org/mamba/blob/ab22b6398533bcbd01f7642f7921636facbb6cfa/libmamba/src/api/configuration.cpp#L456 it should probably pick the first writable envs dir provided