Create a new option for metrics calles "graph", which takes graph objects as a csr adjacency matrix and runs the HDBSCAN function on the csgraph min_span_tree of the given graph.

Example plot file (plot_hdbscan_graph.py) shows the working of the function and displays the example plots of the graphs.

Modifed the _hdbscan_sparse_distance_matrix function to integrate the graph metric into the hdbscan code.

Started working on the test for the graph metric.

Use the test_hdbscan_sparse_distance_matrix test to create the test_hdbscan_graph function. Added the requirments for the metric to the requirements.txt (igraph and networkx).

Added commentary and proving the test.

Set requirements back to the latest HDBSCAN version.

Co-authored-by: Isaac Virshup <ivirshup@gmail.com>

Updated the hdbscan_ function for metric="graph" and test_hdbscan by integrating the comments made by ivirshup

Removed the networkx as nx import from the test_hdbscan file to avoid test failures, as it wasn't used.