add MSE and MAE metrics - V2
Created a new pull request to resolve unrelated changes in PR caused due to rebasing.
Ref Older PR :  [#3845](https://github.com/huggingface/datasets/pull/3845) 

Feature request here : Add support for continuous metrics (RMSE, MAE) [#3608](https://github.com/huggingface/datasets/issues/3608)