Added benchmarking code for unweighted bellman-ford

[MichaelC101]

Fixes issue:

Fixes issue 6354

Changes:

Created a new bellman-ford cpp file that gives the user the option between creating an unweighted graph and a weighted graph for the purpose to timing bellman-ford on graphs on graphs of different sizes. Includes code from original bellman_ford.cpp in terms of creating the weighted graph.