Add dataset: Decontaminated BEIR

[Samoed]

dataset link on Hugging dataset

https://huggingface.co/datasets/lightonai/arguana-decontaminated

Arxiv link

https://huggingface.co/blog/lightonai/denseon-lateon#decontaminated-beir

Description of the dataset

Cc @NohTow

[NohTow]

Thanks!
ccing @raphaelsty as he is the creator of the dataset!

[raphaelsty]

Thank you @Samoed, it's always really nice to get a ping from you when integrating datasets ☺️