Introduce subset_name as an alias of config_name

[albertvillanova]

Feature request

Add support for subset_name as an alias for config_name in the datasets library and related tools (such as loading scripts, documentation, and metadata).

Motivation

The Hugging Face Hub dataset viewer displays a column named "Subset", which refers to what is currently technically called config_name in the datasets library. This inconsistency has caused confusion for many users, especially those unfamiliar with the internal terminology.

I have repeatedly received questions from users trying to understand what "config" means, and why it doesn’t match what they see as "subset" on the Hub. Renaming everything to subset_name might be too disruptive, but introducing subset_name as a clear alias for config_name could significantly improve user experience without breaking backward compatibility.

This change would:

• Align terminology across the Hub UI and datasets codebase
• Reduce user confusion, especially for newcomers
• Make documentation and examples more intuitive

[aymeric-roucher]

I second this! When you come from the Hub, the intuitive question is "how do I set the subset name", and it's not easily answered from the docs: subset_name would answer this directly.