Add support for USB license keys

[RobotRoss]

As of Flatpak version 1.16.0, --device=usb is now available. See https://docs.flatpak.org/en/latest/sandbox-permissions.html#usb-portal

Add support for accessing USB license keys to the flatpak env by adding the USB portal.

USB device vendor defined to attempt to avoid USB-related crashes Resolve is known to have.

Note that this does require additional udev rules to be added by the user for their system, otherwise DaVinci will segfault on the "Checking Licences..." splash screen. An example udev rule is below:

# Allow Flatpak apps to access USB devices with vendor ID 096e (Feitan Technologies), needed by DaVinci Resolve Studio when using USB licence keys
# Place this file in /etc/udev/rules.d/
# Recommended file name: 99-davinci-usb.rules

SUBSYSTEM=="usb", ATTR{idVendor}=="096e", TAG+="uaccess"
SUBSYSTEM=="usb", ATTR{idVendor}=="096e", MODE="0664", GROUP="plugdev"