Document propOmega, flip thruster, fix coefficient

[chapulina]

• Builds on top of Use upstream's Thruster plugin #74
• Requires Thruster plugin: add tests and velocity control gazebosim/gz-sim#1190
• Last part of Document / update coordinates and units #48
• Closes [Thruster plugin] Flip sign direction. #20

---

The propeller joint's axis was pointing to the vehicle's back, which caused the vehicle to be propelled forward for negative thrust forces. This PR flip the axis so that clockwise rotations when looking from the back cause the vehicle to move forward:

• Documented propOmega
• Flipped the propeller joint, and flipped the commands accordingly
• Fixed the conversion from angular velocity to force. The formula on TethysComm was using 0.0016 m for the propeller diameter, but the Thruster uses 0.2 m, taken from the SDF. I updated TethysComm to use 0.2 m, and that made the vehicle extremely fast. So I reduced the coefficient 100x to compensate.
  • As described on Update Thruster to also accept angular velocity commands #75, we're converting from ang vel to force and back. It would reduce errors if we only converted once.
• Updated a few test expectations to the new thrust. In particular, yoyo is spinning a bit faster now. I also took the opportunity to add more checks to yoyo, and make the tolerances tighter (from 12 m / 1.57 rad to 1.5 m / 0.1 rad!!!) and remove the specific trajectory check, because it was too hard to maintain and failures weren't useful 🪀

[arjo129]

Thanks for these changes. The PR Looks Good To Me.