[ENH] read .env file for environment variables

[AlbertDeFusco]

Currently a user can define local values of variables defined the anaconda-project.yml file in a file called anaconda-project-local.yml. It seems reasonable to also support a more standard approach with a .env file in the project directory.

Does anyone reading this have a strong opinion about which one would take precedence if both a .env and anaconda-project-local.yml file are present?

[jbednar]

I would think anaconda-project-local.yml would take precedence, as it's the one more specific to a-p, and the most specific should normally be the final word (and the least used).

Should the title be read .env file for environment variables?