[ENH] - Consider using OS-specific standards for conda-store data

[jaimergp]

Feature description

As part of #513, it was suggested to use ~/.conda-store as the default data directory. This was implemented successfully in #639.

I am suggesting we stick to well defined standards for this kind of decisions, instead of polluting the home directory with one more dot-folder. Namely:

• On Linux, follow XDG Base Directory Specification
  
• On macOS, it seems that CLI apps still follow XDG standards as Linux. GUI stuff drops things in ~/Library. See this SO thread.
• On Windows, we should probably use %LOCALAPPDATA% (i.e. non-roaming).

Value and/or benefit

Following well established standards in each Operating System allow us to be better citizens, and navigate better known spaces (e.g. permissions, lack of user profiles in some Windows installations).

A nice side effect, and one of the reasons these standards exist, is to avoid polluting the user profile with dot-directories.

Anything else?

Comes from #639 (comment)

[nkaretnikov]

ArchWiki list, with links to various issues: https://wiki.archlinux.org/title/XDG_Base_Directory_support

[costrouc]

Yeah totally agree we should use system defaults

[jaimergp]

conda is going to switch to platformdirs (instead of the vendored appdirs), which seems to abstract away all the complicated business:

https://platformdirs.readthedocs.io/en/latest/index.html

[nkaretnikov]

Status update: not working on this until other issues in the milestone are resolved.