Use plugin architecture for loading the backends

[francocipollone]

Summary

Maliput provides a plugin architecture for loading RoadNetworks using different backends.

Victory Condition

Remove build dependency on maliput_dragway, maliput_multilane and maliput_maldirive and load them as a plugin.

Examples

It is already being used in delphyne. See and maliput_viz

[francocipollone]

This will require removing the particular gflags for each maliput backend. As they are loaded in runtime, any user should be able to use their own maliput backend implementation.

For loading the parameters we could pass a yaml, similarly to what we do with the maliput_viz package:

  * YAML file configuration:
     The --yaml_file_path flag expects a valid path to a YAML file.
     The YAML file should contain the configuration for loading the road network.
     The structure of the YAML file should be:
      |  maliput_viz:
      |    maliput_backend: <backend_name>
      |    parameters:
      |       <key_1>: <value_1>
      |       <key_2>: <value_2>
      |       ...
      |       <key_N>: <value_N>

wdyt? @agalbachicar

[agalbachicar]

Remove build dependency on maliput_dragway, maliput_multilane and maliput_maldirive and load them as a plugin.

I think we should have examples that show how to avoid the plugin infrastructure as well.

[agalbachicar]

For loading the parameters we could pass a yaml, similarly to what we do with the maliput_viz package:

I am OK with this.