Xtreme-S Metrics
@lhoestq - if you could take a final review here this would be great (if you have 5min :-) )  Don't think the failures are related but not 100% sure Yes the CI fail is unrelated - you can ignore it
**Added datasets (TODO)**:

- [x] MLS
- [x] Covost2
- [x] Minds-14
- [x] Voxpopuli
- [x] FLoRes (need data)

**Metrics**: Done