Provide some lever for controlling installer error logging in CI environments

[brian-dlee]

• I have searched the issues of this repo and believe that this is not a duplicate.
• I have searched the FAQ and general documentation and believe that my question is not already covered.

Feature Request

Provide some kind of environment variables to control the Poetry installer's logging. The installer script installs to a poetry-installer-error*.log file, but in CI environments this can be painful to debug. There should be some kind of lever to pull to get poetry to output the installation errors directly to stderr.

Many packages automatically detect the CI variable (standard among the CI providers from what I can tell) to automatically change configuration parameters.