LunarSim

Resolves #50, depends on space-ros/docs#36

This PR adds a Gazebo Garden based lunar world demo to spaceROS. The features included in this PR are:

• A world with a lunar terrain that is derived from a Digital Elevation Model (DEM) of the area around the Shackleton Crater (close to the South Pole) taken from the Lunar Orbiter Laser Altimeter (LOLA).
• A dynamic model of the Sun that accurately depicts the low light conditions near the lunar south pole by using ephemeris data from NASA's Horizons application.
• Improved lunar surface texture created by blending surface normals with high resolution sand texture.

This package serves as a foundation for creating a realistic lunar simulation that the community can further expand upon. To support this, we have provided comprehensive documentation that guides users through the process of preparing and adding their own DEMs, ephemeris data, and custom textures. These tutorials can be found in our space-ros/docs PR ( space-ros/docs#36)

Instructions on how to run the demo can be found in the README. This image builds on top of the spaceROS base image and follows the format used in other demos for consistency.