Checklist

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

What is the idea?

conda-standalone should become vendor agnostic by default (see conda/conda#14217 for context).

Why is this needed?

conda-standalone binaries currently point to Anaconda's defaults channel, even if they are build by conda-forge. Additionally, conda will deprecate using Anaconda's defaults channel as a fallback.

What should happen?

One (or both) of these options should be implemented:

1. Add a warning or error when channels are not explicitly set when invoking conda-standalone.
2. Inject channel URLs when building the conda-standalone conda package.

Additional Context

No response