Add Elastic Costs again or asses if they are necessary or not

[selmanozleyen]

In this PR #725 I removed the Elastic cost functions since ottjax removed them with this commit: ott-jax/ott@d5d8a47

We should decide what we are going to do about this

[marcocuturi]

@michalk8 I think this should be easy?

[michalk8]

Yes, they've been refactored to just use RegTICost + a regularization class; should be fairly easy to incorporate the changes.

[selmanozleyen]

if then necessary we'll add it, so I am closing this issue for now. Just wanted to know how important it was to replace them and their removal is documented