[FEATURE] Cluster junctions by hierarchical clustering

[Irallia]

Hierarchical clustering is the clustering method employed by SVIM. It will be implemented in src/modules/clustering/hierarchical_clustering_method.cpp.

Steps:

1. Generate partitions of junctions lying close to each other on the reference genome (clustering is O(n^2) so it's much faster on a small partition than the entire genome)
2. Cluster the junctions in each partition using agglomerative hierarchical clustering

We could use https://github.com/cdalitz/hclust-cpp as an existing implementation for the 2nd step.