iwd has been good enough for a long time we still need to check whether it has feature parity with wpa_supplicant

Due to the issues of v2.10 of wpa_supplicant we'll start providing iwd as an opt-in replacement for it.

To enable iwd:

• Package iwd
• Enable support for iwd in NetworkManager by passing iwd=true to meson configure.
• Users will have to manually create /etc/NetworkManager/conf.d/wifi_backend.conf with

[device]
wifi.backend=iwd

and enable the iwd service to use iwd in place of wpa_supplicant.

We could configure iwd to be enabled automatically in NetworkManager if it is installed.