Demonstrate sensor head construction with test point connection

[robrussell]

The camera sensor head holds the Raspberry Pi HQ camera. It's pretty clear how the 3d-printed parts mate together but the details of the sync connector are not obvious. The HQ camera board exposes test points for the IMX477 which allow XVS to be shared between multiple sensors. Constructing the sensor head correctly requires soldering leads between the test points and the TRS connection on the camera extension PCB. Document and photograph the construction.