flatten the "playbooks" directory for better structure

Because of how Ansible local relative search paths work, the global
"files" and "templates" directories need to be next to the playbooks.
However its not intuitive to look into the playbooks directory to find
the files and templates for a host.
Therefore flatten the playbooks directory to get rid of this confusing
structure.

Also see:
https://docs.ansible.com/ansible/latest/playbook_guide/playbook_pathing.html#resolving-local-relative-paths

roles/apt_update_and_upgrade/README.md

@@ -0,0 +1,11 @@
+# Role `apt_update_and_upgrade`
+
+This role does an `apt-get update`, `apt-get dist-upgrade` and a potential reboot (if packages got upgraded) on the specified hosts.
+
+## `hosts`
+
+The `hosts` for this role need to be the VMs, which should be updated and upgraded.
+
+## Required Variables
+
+This role doesn't have any required variables.

roles/apt_update_and_upgrade/handlers/main.yaml

@@ -0,0 +1,3 @@
+- name: reboot the system
+  become: true
+  ansible.builtin.reboot:

roles/apt_update_and_upgrade/tasks/main.yaml

@@ -0,0 +1,13 @@
+- name: update, upgrade and potentially reboot
+  become: true
+  block:
+    - name: apt-get update
+      ansible.builtin.apt:
+        update-cache: true
+
+    - name: apt-get dist-upgrade
+      ansible.builtin.apt:
+        upgrade: dist
+      register: apt_update_and_upgrade__upgrade_result
+      notify:
+        - reboot the system