Attach `duration` and `distance` to `intersection` array

[daniel-j-h]

Our intersection array represents the intersection for the maneuver plus any additional intersections the user crosses until the next maneuver: http://project-osrm.org/docs/v5.7.0/api/#intersection-object

In case clients want to tell users to stay on a specific lane or keep going straight at intermediate intersections they need the distance and duration (and weight?) for deciding when to announce this.

Therefore we need to attach distance and duration to the intermediate intersections for clients:

Tasks:

• [ ] augment route step assembly with distance, duration (, weight ?)
• [ ] add changelog entry
• [ ] adapt docs/http.md