Ignore .condarc files during installation

[marcoesters]

Description

conda-standalone and micromamba load existing .condarc files during the installation process, which can have unintended consequences and even break the installation. These issues have been frequently reported (see #542, #568, and the issues reported therein). The behavior of the installer should be set by the installer itself and not by residual configuration files, especially since they are not cleaned up at all (see #642).

micromamba has a --no-rc option, which is also proposed to be added to conda-standalone (https://github.com/conda/conda-standalone/pull/99). This feature will add the --no-rc option with compatible standalone executables.

Closes #542 and #568.

Checklist - did you ...

• [X] Add a file to the news directory (using the template) for the next release's release notes?
• [X] Add / update necessary tests?
• [X] Add / update outdated documentation?

[marcoesters]

Even if approved, we should probably wait with merging this until conda-standalone 24.9.x is released and I had the chance to re-run the tests.

[jaimergp]

Seems to be working @marcoesters