add sugar for modifying kernel arguments

[dustymabe]

For our cgroup v2 strategy ticket, we identified that we need an easy way for a user to be able to set kernel arguments for many reasons, but also to toggle cgroups v2 on and off.

We need the ability for a user to easily configure kernel arguments and also documentation on how to do that.

[jdoss]

Any ETA on when this is going to be considered? Using FCOS with rootless podman with cgroups v1 is very painful.

[lucab]

No ETA that I am aware for this at this point, but I don't expect this feature to land anytime soon.

As noted in coreos/fedora-coreos-tracker#292 (comment), there is quite a bit of groundwork to be done at initrd/ostree/ignition level.
Once the primitives are in place there, the sugar here should be relatively straightforward to wire.

[bgilbert]

This is done in fcos spec 1.4.0 and documented in FCOS.