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)

首先定位 issue 中描述的 assignment 输出路径和车辆路线遍历。检查针对每个位置索引如何读取 capacityDimension.CumulVar(index)，然后验证输出是否包含每辆车在服务每个位置之前和之后的容量。