Extend PclConverter for loading a color layer from a textured mesh

[Jaeyoung-Lim]

Problem Description
When loading a gridmap from a polygon mesh, only the geometry was being read on the grid map.

This commit extends the gird map pcl coverter for loading a color layer from a textured mesh

This is useful when loading colored pointclouds or reconstructions on the grid map for visualization purposes

Testing
A mesh can be read and added with a color layer with the two sequences

  grid_map::GridMapPclConverter::addLayerFromPolygonMesh(mesh, "elevation", grid_map_);
  grid_map::GridMapPclConverter::addColorLayerFromPolygonMesh(mesh, "color", grid_map_);

[Jaeyoung-Lim]

@maximilianwulf The CI Build failure doesn't seem to be related to this PR?

[Jaeyoung-Lim]

@Ryanf55 Could we get this in?

[Ryanf55]

@Ryanf55 Could we get this in?

Sorry, I only have merge authority for ROS2 branches. Let's kindly ask @maximilianwulf to take a look.