[FEAT] Add EWCA in to ot.dr

[antoinecollas]

Types of changes

Add function ewca into ot.dr module.

Motivation and context / Related issue

Add dimensionality reduction method called Entropic Wasserstein Component Analysis from the paper https://arxiv.org/abs/2303.05119.

How has this been tested (if it applies)

Add a test in test/test_dr.py that checks that the ewca function estimates the first and last principle components when its regularisation parameter is low and high, respectively.

PR checklist

• I have read the CONTRIBUTING document.
• The documentation is up-to-date with the changes I made (check build artifacts).
• All tests passed, and additional code has been covered with new tests.
• I have added the PR and Issue fix to the RELEASES.md file.