add turris "schnapps" tool

in its current state this is useful for turris omnia only, but will
allow us to do installs and rollback to turris os if needed.

modules/schnapps/default.nix

@@ -0,0 +1,19 @@
+{ config, pkgs, lib, ... } :
+{
+  config = {
+    programs.busybox = {
+      options = {
+        # schnapps is a shell script that needs
+        # [ command
+        # find -maxdepth  -mindepth
+        # head -c
+        # echo -n
+        ASH_TEST = "y";
+        FEATURE_FIND_MAXDEPTH = "y";
+        FEATURE_FANCY_HEAD = "y";
+        FEATURE_FANCY_ECHO = "y";
+      };
+    };
+    defaultProfile.packages = [ pkgs.schnapps ] ;
+  };
+}