BackendV2 coupling map should be iterable

[nonhermitian]

What should we add?

Iterating over the edges of a coupling map is really one of the primary use cases for dealing with this object outside of the transpilation stack. As it stands now, I need to remember that cmap.get_edges() must be called for V2 but not V1. Printing the coupling map from V2 shows a nested list, so naively I would expect to be able to directly iterate on it.

[jakelishman]

It will be iterable in 0.23, since we added it (#9051) the last time you opened this issue (#8863).