Allow user to override the built-in `grayskull_pypi_mapping`

[tombenes]

Checklist

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

What is the idea?

Allow the user to override the built-in default grayskull_pypi_mapping with a cli argument like --override-name-mapping, providing a json file to use instead of the build-in one.

Why is this needed?

Current built-in mapping contains a map from pypi to conda-forge name. Some package names differ between conda-forge and anaconda official channel.

What should happen?

User should be able to override the built-in map with a CLI argument.

Additional Context

I'm currently working on this feature.

[dholth]

Would also be nice to allow pyproject.toml to have a say in that particular package's name in conda-land...