Add Nix installation

ansible/roles/install_nix/tasks/main.yaml

@@ -0,0 +1,17 @@
+---
+# Obvious race condition here that we are just going to ignore
+- name: Copy Nix installation script
+  become: yes
+  ansible.builtin.copy:
+    src: install-nix
+    dest: /etc/pbri/install-nix
+    owner: "{{ ansible_user }}"
+    group: "{{ ansible_user }}"
+    mode: "0755"
+# --daemon: multi-user installation
+# < /dev/null: Stops the script asking for permission
+- name: Run Nix installation script
+  ansible.builtin.shell:
+    cmd: /etc/pbri/install-nix --daemon < /dev/null
+  args:
+    creates: /nix