Thanks again for your help with this. I got a 10 pack of servo plugs from Amazon.
This evening, I spent some time considering camera settings, and how I want it to be set when flying. The manual for the camera is very long, and there is quite a bit of flexibility in the design of the camera, most of which will not be controllable by the Pixhawk. So, I have chosen to take photos in "Smart Mode - Landscape", which seems most appropriate for aerial photography (still subjects).
I also experimented some more with the auto focus and camera triggering to see how it might be affected by the servo circuit. I have decided to set the camera for a single auto focus before taking a picture. When I connect the PLS and GND wires, I confirmed that the camera focuses on the subject before taking the picture, and thus there is no need to separately control the focusing prior to taking a shot. Also, it doesn't matter how long I hold the PLS and GND wires together - it will only take one shot whether connected for a small fraction of a second or for several seconds. So, your suggested setting of 1 second should work just fine.
I was reading through a manual related to aerial photogrammetry software that I have, and it suggests that the orientation of the picture (i.e. portrait or landscape) may affect the processing of the photos. Landscape is recommended, and switching between landscape and portrait is not recommended. So, I will have to mount the camera on the drone so that it will take landscape photos in flight.
I'm excited to build the simple circuit you have so kindly explained to me.
I'll keep you posted.