[Clustering] Create/Add an additional trainer for Clustering: Affinity Propagation

In ML.NET we currently only have the [KMeansTrainer](https://docs.microsoft.com/en-us/dotnet/machine-learning/resources/tasks#clustering).

The main challenge with that clustering trainer is that you need to provide the number of clusters to use (numberOfClusters param also known as k), and that's a very difficult number to figure out. THere are methods that can help, like the Elbow method, but still it is a challenge.

There are other clustering algorithms that doesn’t require in input the number of expected clusters like the **Affinity Propagation** algorithm.
It is relatively new (Presented in 2007) and it works by measuring the affinity between data items.

Further info about it:
https://towardsdatascience.com/unsupervised-machine-learning-affinity-propagation-algorithm-explained-d1fef85f22c8

The function that measures affinity between data items is one of the hyperparameters of the algorithm.

**Affinity Propagation is an unsupervised machine learning algorithm that is particularly well suited for problems where we don’t know the optimal number of clusters.**

As an additional note, consider that K-means was first proposed for application in the field of statistics back in 1955.

I suggest that, when possible, we implement and offer this additional clustering algorithm, especially when we currently just have one algorithm for Clustering (KMeansTrainer).