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.

pkgs/schnapps/default.nix

@@ -0,0 +1,27 @@
+{
+  stdenv
+, fetchFromGitLab
+, makeWrapper
+, btrfs-progs
+, lib
+}:
+let search_path = lib.makeBinPath [btrfs-progs];
+in stdenv.mkDerivation {
+  pname = "schnapps";
+  version = "2.13.0";
+
+  src =fetchFromGitLab {
+    domain = "gitlab.nic.cz";
+    owner = "turris";
+    repo = "schnapps";
+    rev = "53ac92c765d670be4b98dba2c948859a9ac7607f";
+    hash = "sha256-yVgXK+V2wrcOPLB6X6qm3hyBcWcyzNhfJjFF7YRk5Lc=";
+  };
+
+  nativeBuildInputs = [ makeWrapper ];
+  buildPhase = ":";
+  installPhase = ''
+    install -D schnapps.sh $out/bin/schnapps
+    wrapProgram $out/bin/schnapps --prefix PATH : "${search_path}"
+  '';
+}