nk3: Improve error message for missing udev rules

[robin-nitrokey]

Trying to use the bootloader without the proper udev rules raises a unhandled SPSDKConnectionError. We should show a proper error message linking to the udev docs instead.

[daringer]

it might be worth extracting the detection part into the nk-sdk for easy availability inside NitrokeyApp2, I'd see the following detectors ("connectivity tests" ?)

• detect existence of proper udev rules for nk3, nkpk (actual string in expected file location(s))
• if device plugged in, actually verify permissions for device (maybe with bootloader test?)
  • udevadm test $(udevadm info -q path -n /dev/hidraw9) lists:
    • read udev rules
    • indicators if rules have been applied
• detect snap and detect snap rules, see Add Nitrokey identifiers to relevant (Ubuntu) Snaps' udev rules nitrokey-3-firmware#573
• detect gpg(-agent) exclusivity (?)
• detect usbguard

[robin-nitrokey]

I’m still skeptical if it makes sense to try such a detailed analysis. I think it’s easy to get the details wrong and show false positives. From my experience, in 99 % of the cases, the udev rules are just missing. Or do you have a different experience in support?