Add different greedy strategies for node coloring

[alexanderivrii]

What is the expected enhancement?

This tracks the rustworkx part of Qiskit/qiskit#11779 (comment). The request is to add other standard greedy node coloring strategies, such as the "saturation first" strategy: always picking the node that has the largest number of different colors assigned to its neighbors, and, in case of a tie, the node that has the largest number of uncolored neighbors.

This will be immediately followed up by a PR.