Camera backpack carabiner mount

New version (backpack_mount3): I re-designed the part that keeps the carabiner in place on the stripe. This new version uses normal PLA (instead of flexible) and should stay better in place and be more durable.

Secure carabiner mount for a dslr camera. It uses my [carabiner design](https://www.thingiverse.com/thing:4222280) which can sustain my own weight.

The carabiner is fixed to the backpack strap with a flexible plate (printed in flex PLA).

On the camera side, the loop is secured with a camera screw such as [this one](https://www.amazon.fr/gp/product/B00MGMM99K/) with a rubber joint inbetween to prevent unscrewing. There is a small bump so that the screw cannot untighten without rotating the part itself.