Move solo2 udev rules into it's own directory

[JohnPeacock]

Support for Ubuntu to install udev rules (much like the original solokeys repo supports).

Verified that it can be used to flash the most recent firmware:

$ solo2 update
Downloading latest release from https://github.com/solokeys/solo2/
Fetched firmware version 2:20220822.0 (2.964.0)
Tap button on key to confirm, or replug to abort...
LPC55 Bootloader detected. The LED should be off.
Writing new firmware...
Done. Rebooting key. The LED should turn back on.

[nickray]

There are a lot of instructions scattered in the internet pointing to the original udev rules file location.
Willing to merge this if you keep the file as is, and just point to it from your udev/Makefile.

The really nice solution I hope we arrive to (at some point...) is for distribution packages that handle this.
That is, a solo2-cli package with solo2-udev dependency package, on the Debian/Fedora/Ubuntu/... platforms (similar to https://aur.archlinux.org/packages?K=solo2-cli). Plus solo2 somehow probing udev to check if necessary things are accessible.