Expose RoadNetwork configuration builder keys.

[francocipollone]

Summary

Related to https://github.com/ToyotaResearchInstitute/maliput_malidrive/issues/187

• Expose RoadNetwork configuration builder keys. -->
  • #include malidrive/builder/params.h defines the keys

• Docstring related to load method was refactored:

  • malidrive::loader::Load doc: --> Links to RoadNetwork configuration builder keys group

  • RoadNetwork configuration builder keys group under malidrive::builder::params: --> There is a submodule " RoadGeometry configuration builder keys "

  • RoadGeometry configuration builder keys group

[francocipollone]

I will wait for @liangfok 's approval before merging, as this feature was requested by him. Just in case there is something else that could be added to benefit downstream projects.