[GCS] SolveTravelingSalesperson, SolveSpanningTree, etc.

[RussTedrake]

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In @TobiaMarcucci 's thesis and in gcspy, he has developed the GCS transcriptions of many common problems that can be formulated on a graph:

• [ ] SolveTravelingSalesperson
• [ ] SolveSpanningTree
• [ ] SolveFacilityLocation (which can be used, e.g. for generating sphere collision geometries from a mesh)

and the catch-all

• [ ] SolveFromILP

My aim is to support all of these in Drake, too.