[ENH] Elastic-SOM clusterer

[chrisholder]

Reference Issues/PRs

#2130

What does this implement/fix? Explain your changes.

This PR implements the Elastic-SOM clusterer. SOM is a neural network that iteratively updates weights between input neurons (time points) and output neurons (cluster centres). The algorithm has been proposed for use with DTW and the use of the DTW alignment path. Our implementation supports all the distances avaliable in aeon.distances.

Does your contribution introduce a new dependency? If yes, which one?

Any other comments?

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