Implement triangle count

[DoganCK]

Description
The Triangle Count algorithm counts the number of triangles for each node in the graph. A triangle is a set of three nodes where each node has a relationship to the other two. In graph theory terminology, this is sometimes referred to as a 3-clique. The Triangle Count algorithm in the GDS library only finds triangles in undirected graphs.

Pointers
The clustering coefficient makes use of triangles, which might give some ideas about the implementation.

References
https://neo4j.com/docs/graph-data-science/current/algorithms/triangle-count/