Support Conda

[lolpack]

The typechecker and IDE should be aware of conda virtual environments when configured by the user. The runtime and packages that are installed where.

[connernilsen]

How to get this working for now

If you have conda set up locally, you can get Pyrefly working with it by having your Conda environment
sourced in your shell (conda activate <environment>), and we will automatically pick up your installed packages.
To pick up your packages even when your environment isn't sourced, you can query your environment's install
location with conda env list, and add <conda_environment_path>/bin/python3 to your Pyrefly configuration
under python_interpreter or pass it in with the --python-interpreter flag.

NOTE: You'll likely want to remove this from your config once we get auto-venv working, since
it may make your configuration more difficult to use on different systems.