CTAP2 BLE support

[jo-bitsch]

I am currently working on adding support for CTAP2 BLE to libfido2 in linux.

I got some initial work done based on libsystemd to connect to Bluez via D-Bus. A proof of concept is working with device enumeration and discovery working ok so far.

Are there any thoughts here on this.

libsystemd itself is not dependent on the underlying system running systemd, so that should also work on non-systemd systems like alpine, which provides a compatible library under libelogind.

Would there be any fundamental blockers to merging such a PR, or any points where you would like me to be particular careful to ensure such a PR goes as smooth as possible.

[jo-bitsch]

Just noticed #700 So this is already being worked on