[RFE] Create a systemd-sysext for extra, on-demand load Linux drivers

[ader1990]

Current situation

Flatcar is a generic minimal operating system.
But sometimes, mostly when running on various hardware, the Flatcar Linux kernel needs to contain niche drivers in order for the user to leverage those hardware devices like i/GPUs, Bluetooth devices, WiFi cards, etc.

Impact

The user needs to ask Flatcar maintainers to enable the driver to be built, and the drivers need to be, from then on, on every image, although in most use-cases, those drivers will not be used.

Ideal future situation

In order to keep the core system size minimal, users need to have a way to build and add those drivers when needed.

Implementation options

I suggest to create a systemd sysext called linux-extra-drivers, where to just add those drivers when community needs them.

I have opened this thread as there was recently a set of opened issues / PRs on this topic:

#1306
#1535
#1556

Note: some drivers are required by the initrd stage - like the network and storage ones, this feature request is not about those ones, as those drivers need to be enabled and included in the official Flatcar images. Downloading a sysext requires network connectivity and / or storage (chicken and egg problem).