Make slotcar respect speed limits

[luca-della-vedova]

Feature request

Description

As a part of our ongoing effort in implementing speed limits in lanes we should add support in slotcar for respecting lanes speed limits.

Implementation considerations

A possible approach involves adding a new parameter to mode request to set the speed and have the robot subscribe to it, an alternative would be to parse the navgraph at the slotcar level and keep track of the lane the robot is in and its speed limit.