Document the `linux.override` way first, then `linuxManualConfig`.
Add a `linux.configEnv` passthru attribute for quickly getting a
`make nconfig`-ready shell.
I'm well aware that this issue is currently under discussion[1] and that
these things may change. Also, please don't misinterpret this as an
attempt to end the discussion.
This topic made it obvious that people are surprised by the way this
issue is handled and only finding out about this unwritten rule because
of asking is not a good state IMHO, so I decided to document the
following things:
* Right now we drop kernels as soon as they get out of maintenance (LTS
kernels even before the next stable NixOS that will exceed their
lifespan).
* The `latestCompatibleLinuxPackages` attribute from ZFS isn't
monotonic since latest only refers to the latest supported kernel.
* In fact `latestCompatibleLinuxPackages` doesn't seem to be documented
at all in the manual, so I also did that.
[1] https://discourse.nixos.org/t/aggressive-kernel-removal-on-eol-in-nixos/23097
