make python user site-packages isolation in .local directory configurable #7707
Description
As described in #7671 (comment)
For activated non-base conda environments, conda activate will actually go ahead and set the PYTHONNOUSERSITE environment variable, I'm suggesting you do now yourself. By default it will not set it for the base environment, whether the base environment is properly activated or not. This behavior will all be configurable, and there appear to be three states to what we're proposing for python interpreter isolation from ~/.local: disabled, non-base, all. The default value for the configuration, as proposed, would be the non-base one.