Add Focuser Example for PyQt Applications

[msalmonw]

Added an Example PyQt Application which utilizes the focuser script and the libcamera preview window. The preview window is embedded in the PyQt Application through the window ID of the libcamera preview window.

To find the window ID of any external window for embedding in your application, use 'xwininfo'.

NOTE: This script doesn't use picamera2 library because it mostly has memory issues on weaker Raspberry Pi models. This is based on my own workaround for using the libcamera library directly and embedding it in the PyQt application.