Add OffComBR
Add [OffComBR](https://github.com/rogersdepelle/OffComBR) from [Offensive Comments in the Brazilian Web: a dataset and baseline results](https://sol.sbc.org.br/index.php/brasnam/article/view/3260/3222) paper.

But I'm having a hard time generating dummy data since the original dataset extion is `.arff` and the [_create_dummy_data function](https://github.com/huggingface/datasets/blob/a4aeaf911240057286a01bff1b1d75a89aedd57b/src/datasets/commands/dummy_data.py#L185) doesn't allow it.