Nix task

Closes #3

roles/common/tasks/main.yml

@@ -2,3 +2,4 @@
 - include: selinux.yml
 - include: packages.yml
 - include: users.yml
+- include: nix.yml

roles/common/tasks/nix.yml

@@ -0,0 +1,25 @@
+# SPDX-FileCopyrightText: Copyright (c) 2021 Ableton AG
+# SPDX-License-Identifier: MIT
+---
+- name: Ensure nix directory exists
+  become: true
+  file:
+    path: "/nix"
+    owner: "earne"
+    state: directory
+    mode: "0755"
+  register: nix_directory
+
+- name: Install nix
+  block:
+    - name: Download installer script
+      get_url:
+        url: "https://nixos.org/nix/install"
+        dest: "/tmp/install_nix.sh"
+        mode: "0755"
+
+    - name: Run installer script
+      become: true
+      become_user: "earne"
+      command: "/tmp/install_nix.sh"
+  when: nix_directory is changed