Add bcachefs support. Fix clan flash docu.

nixosModules/bcachefs.nix

@@ -0,0 +1,12 @@
+{ lib, pkgs, ... }:
+
+{
+  # Enable bcachefs support
+  boot.supportedFilesystems.zfs = lib.mkForce false;
+  boot.kernelPackages = lib.mkOverride 0 pkgs.linuxPackages_latest;
+  boot.supportedFilesystems.bcachefs = lib.mkDefault true;
+  environment.systemPackages = with pkgs; [
+    bcachefs-tools
+    keyutils
+  ];
+}