Document how auto_inertia_params are handled when specified in both collision and link

[scpeters]

Desired behavior

From gazebosim/sdformat#1335 (comment):

We should document on sdf_tutorials that this works by completely replacing the parameters in the link, i.e, the values inside auto_inertia_params of the collision do not "merge" with the ones lin the parent link.

Alternatives considered

Implementation suggestion

Additional context