Use nominal extrinsics for Realsense D435 camera

[eborghi10]

This PR sets the use_nominal_extrinsics argument to true so the Realsense D435 camera can provide the optical frame Tf.

Steps to reproduce this:

# Launch the simulation
roslaunch ari_2dnav_gazebo ari_mapping.launch public_sim:=true

# Inspect the Tf tree
rosrun rqt_tf_tree rqt_tf_tree

[schizzz8]

@eborghi10 thanks for your contribution. We are reviewing your PR internally!