If only one service use GLOBAL_CHEAPEST_ARC
If only one service use GLOBAL_CHEAPEST_ARC

Due to an or-tools limitation, a single service can only be modelled as
a mandatory service, for which other first_solution_strategy options
sometimes have trouble finding a feasible solution.

Mapotempo/optimizer-ortools,Mapotempo/optimizer-ortools,Mapotempo/optimizer-ortools