Adds base RoadNetwork/RoadGeometry Rust API.

[francocipollone]

🎉 New feature

Related to #30 #31

Summary

Adds Rust API for a minor part of the maliput::api::RoadNetwork/RoadGeometry (cpp) interface.

Checklist

• [x] Signed all commits for DCO
• [ ] Added tests
• [x] Added example and/or tutorial
• [ ] Updated documentation (as needed)
• [ ] Updated migration guide (as needed)
• [ ] Consider updating Python bindings (if it affects the public API)

[francocipollone]

@agalbachicar Note that this case for the RoadNetwork and RoadGeometry is probably not the one that is related to the F2F talk about rust vs cpp ownership and heap allocation In this case we have a road network being created in cpp world and we consume from there. Its allocaiton is in the head and managed by the cpp world. It sounds that therefore makes sense ...:

• Having a RoadNetwrok (Rust) that has a reference to a cpp binding:
  • UniquePtr<maliput_sys::api::ffi::RoadNetwork>
• And having a RoadGeometry (rust) using a reference to the RoadGeometry cpp binding:
  • &maliput_sys::api::ffi::RoadGeometry

A different case happens with simpler structs/classes like LanePosition or InertialPosition. In those cases, having a cpp heap allocation sounds wrong and it is where I should narrow down the search for investigating that use case.