Implement logic to detect whether or not the VxScan accessible input is connected

[arsalansufi]

vxsuite/apps/scan/backend/src/app.ts

Lines 149 to 150 in a278e67

	// TODO: Implement logic to populate this value
	isAccessibilityInputConnected: undefined,

This relates to cert alarm requirements. All the necessary alarm logic is wired up, including the alarm for the VxScan accessible input. We just need to implement the logic to detect whether or not the VxScan accessible input is connected, which is blocked on identifying the accessible input that we want to use. Once we have that, we can check for the expected USB device (by product ID, vendor ID, etc.). We could use an lsusb system call straight from the VxScan backend or a udev rule that has a side effect, like writing to a status file, which we can then check from the VxScan backend. I suspect that the latter will be less costly.

[arsalansufi]

This could end up irrelevant if we end up using an integrated PAT jack. Since all of the accessibility odds and ends are so intertwined and dependent on the hardware that we choose, closing this issue and incorporating into #7499