Camera Guard for HGLRC Arrow3

This provides some camera protection for the HGLRC Arrow 3. The design was integrated with the top plate so that it would work well underneath this [shark fin thing](https://www.thingiverse.com/thing:3748060), but if you don't like that, the fusion source is included so you can try something else. I broke my top plate (and camera) on the first day, so needed a replacement anyway :D

I designed around the bounding dimensions for a Foxeer Predator Micro v4, but if you have a different camera t