Add default ustreamer_desired_fps to hdmi-to-usb config (#1890)

Resolves tiny-pilot/tinypilot-pro#1528

This change sets the default `ustreamer_desired_fps` value for USB
capture devices for better performance with the newer version of
ustreamer.

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Author: db39

debian-pkg/opt/ustreamer-launcher/config-library/hdmi-to-usb.yml

@@ -3,3 +3,4 @@
 ustreamer_encoder: hw
 ustreamer_format: jpeg
 ustreamer_resolution: "1920x1080"
+ustreamer_desired_fps: 30