[MRG] Add CFF file to POT

[rflamary]

Types of changes

POT is used more and more and maintaining it has been quite a job. We need a way to acknowledge all your hard work,
especially for more recent contributors.

Thi PR aim at adding a CFF file (https://citation-file-format.github.io/) to POT and to make a publication of the next release on zenodo to have a proper DOI and to have an updated list of contributors/co-authors that we can ask users to cite. Please contact us if you do not wish to be part of the file or want to update your affiliation. Also, we might have missed some important contributors, so feel free to reach if someone is missing.

Motivation and context / Related issue

How has this been tested (if it applies)

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.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.06%. Comparing base (7019709) to head (9d72b24).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #703   +/-   ##
=======================================
  Coverage   97.06%   97.06%           
=======================================
  Files          98       98           
  Lines       19955    19955           
=======================================
  Hits        19370    19370           
  Misses        585      585