doc: add JPL Horizons example

[jorgepiloto]

This pull-request includes an example for simulating the orbit of Oumuamua interstellar object through the solar system. Ephemerides are retrieved using JPL Horizons API and converted to STK format.

Key topics included:

• Creating a new scenario centered in the Sun
• Using JPL Horizons API
• Conversion to STK ephemerides format
• Visualization tricks to ensure that a large scene renders as expected
• Exposes the scene as a property of plotter