Reduce Simulation Container Sizes

This PR reduces the size of the core starling simulation containers by removing build artefacts and introducing multi-stage builds.

In particular:

starling-sim-base-core is now reduced from 5.98Gb to 2.97Gb
- the removal of download and installation of default models (should be done by user)
- the removal of ros-foxy-gazebo-ros installation in favour of a single ros-foxy-gazebo-ros-pkgs appears to have reduced library download (I suspect we are still getting multiple of the same library installed...)
- Had a look at building gazebo11 or gazebo-ros-pkgs from scratch, but do not know how to reduce size, have raised a question here: https://answers.gazebosim.org/question/27984/build-and-runtime-dependencies-for-minimal-container/
starling-sim-base-px4 is reduced to 3.09Gb
- Removal of extra simulation bridge repositories from PX4-Autopilot/Tools
- Removal of extra models except sun, gps, iris and r1_rover and any given by env var KEEP_PX4_VEHICLES
- The removal of a number of files from the build_gazebo folder (including the CMakeFiles directory which was 400Mb...). The build env var REMOVE_GAZEBO_LIBRARIES by default removes a number of extra libraries, but can be redefined by the user.
starling-sim-ardupilot-gazebo is reduced to 3Gb by only copying over the core ArdupilotPlugin, models and worlds.
starling-sim-iris is therefore now 3.09Gb
starling-sim-iris-ap is therefore now 3.02Gb
starling-sim-px4-sitl is reduced to 820Mb by only copying over the bin folder and ROMFS
starling-sim-ardu* is reduced to 738Mb by only copying over the build and Tools folders

StarlingUAS / ProjectStarling