Consider external triggering for the global shutter camera

[truher]

as part of our experiments with the Raspberry Pi global shutter camera, we should try external triggering, which would allow an array of cameras to snap time-aligned images, and thereby save quite a bit of processing time downstream to interpolate the telemetry.

https://www.raspberrypi.com/documentation/accessories/camera.html#external-trigger-on-the-gs-camera