Add helper for getting all nix files in a directory

Change-Id: Id383c96f1bd6a1c5760f0bac42083822f103f513
diff --git a/default.nix b/default.nix
index 962a7c7..203d39e 100644
--- a/default.nix
+++ b/default.nix
@@ -1 +1,4 @@
-inputs: { nginx = import ./nginx.nix inputs; }
+inputs: {
+  nginx = import ./nginx.nix inputs;
+  nixFilesIn = import ./nixFilesIn.nix inputs;
+}
diff --git a/nixFilesIn.nix b/nixFilesIn.nix
new file mode 100644
index 0000000..a6102a6
--- /dev/null
+++ b/nixFilesIn.nix
@@ -0,0 +1,5 @@
+inputs: dir:
+let lib = inputs.nixpkgs.lib;
+in map (name: dir + "/${name}") (lib.attrNames
+  (lib.filterAttrs (name: type: type == "regular" && lib.hasSuffix ".nix" name)
+    (builtins.readDir dir)))