This copies the implementation from `gazebo_ros_paths.py` to provide a
way for packages to set resource paths from `package.xml`.

```
e.g.  <export>
          <gazebo_ros gazebo_model_path="${prefix}/models"/>
          <gazebo_ros gazebo_media_path="${prefix}/models"/>
      </export>
```

The value of `gazebo_model_path` and `gazebo_media_path` is appended to `GZ_SIM_RESOURCE_PATH`
The value of `plugin_path` appended to `GZ_SIM_SYSTEM_PLUGIN_PATH`

Signed-off-by: Addisu Z. Taddese <[email protected]>

Signed-off-by: Addisu Z. Taddese <[email protected]>

Signed-off-by: Addisu Z. Taddese <[email protected]>