chore: add nix flake and image

flake.nix

@@ -0,0 +1,77 @@
+{
+  description = "Coder Templates";
+
+  outputs = {
+    self,
+    nixpkgs,
+    flake-parts,
+    systems,
+    ...
+  } @ inputs:
+    flake-parts.lib.mkFlake {inherit inputs;} {
+      imports = [
+        inputs.devenv.flakeModule
+        inputs.nix-gitlab-ci.flakeModule
+      ];
+      systems = import systems;
+      flake = {
+      };
+      perSystem = {
+        config,
+        self',
+        inputs',
+        pkgs,
+        system,
+        ...
+      }: {
+        _module.args.pkgs = import nixpkgs {
+          inherit system;
+          config.allowUnfree = true;
+        };
+
+        formatter = pkgs.alejandra;
+        devenv.shells.default = {
+          imports = [
+            inputs.nix-devtools.devenvModule
+          ];
+          packages = [
+            pkgs.opentofu
+            pkgs.coder
+          ];
+
+          pre-commit.hooks = {
+            alejandra.enable = true;
+          };
+          task = {
+            enable = true;
+            alias = ",";
+            tasks = {};
+          };
+        };
+
+        packages = {
+          nix-coder-image = pkgs.callPackage ./image.nix {};
+        };
+      };
+    };
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+
+    flake-parts.url = "github:hercules-ci/flake-parts";
+    systems.url = "github:nix-systems/default";
+    devenv.url = "github:cachix/devenv";
+    nix-gitlab-ci = {
+      url = "gitlab:TECHNOFAB/nix-gitlab-ci";
+      inputs.nixpkgs.follows = "nixpkgs";
+      inputs.devenv.follows = "devenv";
+      inputs.systems.follows = "systems";
+    };
+    nix-devtools = {
+      url = "gitlab:TECHNOFAB/nix-devtools";
+      inputs.nixpkgs.follows = "nixpkgs";
+      inputs.devenv.follows = "devenv";
+      inputs.systems.follows = "systems";
+    };
+  };
+}