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_file }}"
+    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