modules: system: add boot

And enable mounting `/tmp` as tmpfs by default.

modules/system/boot.nix

@@ -0,0 +1,21 @@
+{ config, lib, ... }:
+let
+  cfg = config.my.system.boot;
+in
+{
+  options.my.system.boot = with lib; {
+    tmp = {
+      clean = mkEnableOption "clean `/tmp` on boot.";
+
+      tmpfs = my.mkDisableOption "mount `/tmp` as a tmpfs on boot.";
+    };
+  };
+
+  config = {
+    boot = {
+      cleanTmpDir = cfg.tmp.clean;
+
+      tmpOnTmpfs = cfg.tmp.tmpfs;
+    };
+  };
+}

modules/system/default.nix

@@ -3,6 +3,7 @@
 
 {
   imports = [
+    ./boot.nix
     ./documentation.nix
     ./language.nix
     ./media.nix