Add random graph generator (#5240)

* added complete graph generator function

* added doctest, type hints, wikipedia explanation

* added return type hint for function complete_graph

* added descriptive name for the parameter: n

* random graph generator with doctest and type hints

* validated using pre-commit

* Delete complete_graph_generator.py

* fixed doctest

* updated following reviews

* simplified the code following reviews

* fixed doctest and solved consistency issues

* consistency fixes