Fix missing entities from modules documentation

In the Doxygen documentation, it seems that many modules are not showing all the entities they should.

An example of this is how all names supposedly added to the aux_tracking group in src/xrt/auxiliary/tracking/t_tracking.h do not appear in the generated docs

This seems to be caused by this snippet which is used in many places.

/*!
 * @ingroup <group>
 * @{
 */

Changing @ingroup for @addtogroup seems to fix it.

Feel free to close this MR if there is a reason for this I ignore or if there is a better solution.