Provide capacities per vehicle at each location in output

We should output the capacity each vehicle has before / after servicing a location.

Use-case: being able to tell the vehicle's load at a specific time and place.

Implementation:

• When an assignment could be found: for each vehicle walk over all location indices in the route
• For each location index store the accumulated capacity domain at this location for the vehicle

const auto* loadVar = capacityDimension.CumulVar(index);
assignment->Value(loadVar)

Start by locating the assignment output path and the vehicle route traversal described in the issue. Inspect how capacityDimension.CumulVar(index) is read for each location index, then verify that the output includes each vehicle's capacity before and after servicing every location.