Fix the `datasets` config parameters
We were using `os.environ` to set the `datasets` parameters, which is supported only if it's done before `datasets` is imported.

However in our case `datasets` is already imported, so the changes have to be made in `datasets.config` directly
Fix the `datasets` config parameters: We were using `os.environ` to set the `datasets` parameters, which is supported only if it's done before `datasets` is imported.

However in our case `datasets` is already imported, so the changes have to be made in `datasets.config` directly