We add missing interface to nauty-genbg, a generator of bipartite graphs.

Nauty's genbg was already compiled and accessible but the interface was missing.

Depends on #33366

CC: @tscrim

Component: graph theory

Author: David Coudert

Branch: 695a667

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/33365