`<export>` and `<build_type>` are missing in `package.xml` for `rtabmap_msgs` package.

[dyershov]

Before the package closing tag https://github.com/introlab/rtabmap_ros/blob/337c494f90d110758f5e60cfe2eede6c3bf7f92a/rtabmap_msgs/package.xml#L24

I believe it is necessary to specify build type as follows:

<export>
    <build_type>ament_cmake</build_type>
</export>

We noticed it due to scrapping error in bazel-ros rules. https://github.com/RobotLocomotion/drake-ros/issues/281#issuecomment-1947658004