Added basic implementation of Barycentre Clustering decomposition

[alberto-santini]

This is a first version of the barycentre clustering decomposition method described here.

Missing:

• Possibility of warm-starting the sub-problem from the master problem solution.
• Possibility of solving the sub-problems in parallel.
• Possibility of nesting decomposition, i.e., further decompose the decomposed problems.

[vidalt]

Dear @alberto-santini, My apologies for the delay on this pull request, I will very soon review the changes and possibly simplify as much as possible the new content to keep the algorithm as crisp and maintainable as possible. I send you feedback ASAP on this !

[vidalt]

Thanks a lot, @alberto-santini. I'm validating the pull request in a new branch dedicated to this feature, so I can review, use CI, and possibly simplify.

[vidalt]

Hello @alberto-santini, I noticed that as I did a merge commit (to integrate it with the most recent changes of the dev branch), Git did not correctly attribute authorship automatically. I did not find an easy fix for that unless we redo the pull request, if you agree, I can continue in the current state, and once we integrate these changes in the dev branch through a stashed commit, I can correctly add your contribution using the "Co-authored-by: " trick in the commit message.