Add node exporter

Closes #218 (closed)

ansible/roles/install_node_exporter/tasks/main.yaml

+---
+- name: Download node_exporter binary
+  ansible.builtin.get_url:
+    url: "https://github.com/prometheus/node_exporter/releases/download/v{{ node_exporter_ver }}/{{ node_exporter_filename }}.tar.gz"
+    dest: "/tmp/{{ node_exporter_filename }}.tar.gz"
+
+- name: Extract node_exporter
+  ansible.builtin.unarchive:
+    src: "/tmp/{{ node_exporter_filename }}.tar.gz"
+    dest: "/tmp"
+    remote_src: yes
+
+- name: Create system group for user account {{ node_exporter_group }}
+  ansible.builtin.group:
+    name: "{{ node_exporter_group }}"
+    system: true
+    state: present
+
+- name: Create system user account {{ node_exporter_user }}
+  ansible.builtin.user:
+    name: "{{ node_exporter_user }}"
+    comment: Prometheus node_exporter system account
+    group: "{{ node_exporter_group }}"
+    system: true
+    home: /var/lib/node_exporter
+    create_home: false
+    shell: /sbin/nologin
+    state: present
+
+- name: Copy node_exporter binary
+  ansible.builtin.copy:
+    src: "/tmp/{{ node_exporter_filename }}/node_exporter"
+    dest: /usr/local/bin/node_exporter
+    remote_src: yes
+    owner: root
+    group: root
+    mode: 0755
+
+- name: Copy systemd unit file
+  ansible.builtin.template:
+    src: node_exporter.service.j2
+    dest: /etc/systemd/system/node_exporter.service
+    owner: root
+    group: root
+    mode: '0644'
+
+- name: Clean up /tmp
+  ansible.builtin.file:
+    path: "/tmp/{{ item }}"
+    state: absent
+  loop:
+    - "{{ node_exporter_filename }}.tar.gz"
+    - "{{ node_exporter_filename }}"
+
+- name: Restart node_exporter service
+  ansible.builtin.systemd:
+    daemon_reload: yes
+    name: node_exporter
+    state: restarted
+    enabled: true