Expand Generators Module

[mtreinish]

What is the expected enhancement?

In #121 we added a new module for graph generators which will create graphs of with a certain layout easily. #121 only added a few different types of graphs with the intention of adding more in the future. We should add more generators to the graph to offer more options for quickly creating graphs. Networkx has a long list of generators that can be used for inspiration on different types of generators to add:

https://networkx.github.io/documentation/stable/reference/generators.html

Also, specifically for a qiskit use case we should make sure that we have generators to cover qiskit.transpiler.CouplingMap.from_line, qiskit.transpiler.CouplingMap.from_ring, qiskit.transpiler.CouplingMap.from_grid, and qiskit.transpiler.CouplingMap.from_full (this was handled by #191)

[mtreinish]

Some generators that would be useful to do as part of this would be to add generators for some layouts that are used for error correction codes like heavy hex and heavy square. (see: https://journals.aps.org/prx/abstract/10.1103/PhysRevX.10.011022 ).

[nahumsa]

I will work on the heavy hex generator.