added cronjob to prune unused docker stuff

roles/docker/handlers/main.yml

@@ -0,0 +1,5 @@
+---
+- name: Restart cron
+  ansible.builtin.service:
+    name: cron
+    state: restarted

roles/docker/tasks/main.yml

@@ -60,3 +60,12 @@
     path: /home/{{ system_user_name }}/docker/
     state: directory
     mode: '0755'
+
+- name: Create cronjob to prune unused docker stuff
+  ansible.builtin.cron:
+    user: "{{ system_user_name }}"
+    name: "prune unused docker stuff every night at 00:15"
+    minute: "15"
+    hour: "00"
+    job: "sudo docker system prune"
+  notify: Restart cron