Support adding `condabin/` to PATH

[jaimergp]

Checklist

• I added a descriptive title
• I searched open requests and couldn't find a duplicate

What is the idea?

constructors supports adding bin (on Windows, Scripts) to PATH, but it's discouraged because it pollutes the executable space.

We should provide an option where the installer only offers to add condabin to PATH, so conda (and mamba) can be in PATH without shell initialization.

Why is this needed?

This Miniforge issue provides a good overview of the rationale: conda-forge/miniforge#453

What should happen?

If "Add condabin to PATH" is enabled in the installer and selected by the user, then $INSTDIR/condabin would be in PATH after the installation.

Additional Context

This could also be tackled in conda as part of conda init, but I think this is cleaner? Shell initialization does not necessarily need PATH entries, and viceversa. Should it be a separate conda subcommand? As a plugin? Part of conda-standalone? Open for feedback though.

[jaimergp]

Writing down some notes here after researching the currently available options in constructor.

We have two sets of configuration options that can affect PATH:

• initialize_conda (paired with initialize_by_default). The behavior is platform dependent:
  • On Unix, it controls whether to run conda init as part of the installation (Unix). This results in a conda shell function being defined for the shell session. When paired with activate_base=true (default),$CONDA_ROOT/bin is also added to PATH (which also contains conda).
  • On Windows, it controls whether to add some specific paths to the PATH. It also removes previous additions to PATH if they happened to be still in the uninstallation registry entries.
• register_python (paired with register_python_default). Windows only. Controls whether to register base's Python as the default Python installation for the user or system.

None of these adds condabin to PATH.

[jaimergp]

conda/conda#14703 landed in conda, so should be available in 25.5.