Mismatch about default collision detector between SDFormat specification and Gazebo Sim documentaion

[xela-95]

Hi,

I noted that the SDF documentation about the default collision detector is different from the Gazebo sim one:

• SDF says fcl: http://sdformat.org/spec?ver=1.11&elem=physics#dart_collision_detector
• Gazebo sim says ode: https://github.com/gazebosim/gz-sim/blob/6cfcd07c346a72546963ed56ade48daa828c2072/tutorials/physics.md?plain=1#L100 (also used in unit tests https://github.com/gazebosim/gz-physics/blob/7d30e47fb61fe4db9cba460717a3910df9deabee/dartsim/src/WorldFeatures_TEST.cc#L87)