Nonexistent conda-forge.yml should raise an error

[ytausch]

Comment:

Currently, lint-recipe does not raise an error (lint) if conda-forge.yml does not exist in one of the supported locations relative to the recipe directory. Instead, the configuration is read as empty mapping, which is valid with the Pydantic schema that we currently use.

I don't see any use cases for a conda feedstock that does not contain a conda-forge.yml file.

I see the possibility of undetected errors because of a wrongly placed conda-forge.yml file that is not found by conda-smithy.

Therefore, I suggest raising an error in this situation. If someone really does not want to change the defaults, they should be obliged to create an empty conda-forge.yml file to make their intentions clear.