chore: Add a simple playbook to bring down the site (#266)

### Summary

This is required, for example, if a DB upgrade is necessary.


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Chores**
* Added comprehensive automated infrastructure management system for
containerised application services across all deployment servers.
Enables streamlined and efficient operational procedures for managing
service lifecycles, including proper shutdown and resource cleanup
capabilities. Supports enhanced system maintenance processes, improved
operational consistency, and overall deployment reliability across the
entire production infrastructure environment.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: martyngigg

infra/ansible/site_down.yml

@@ -0,0 +1,17 @@
+---
+- name: Bring down all containers
+  hosts: all
+  tasks:
+    - name: Stop all running Docker containers
+      ansible.builtin.shell: |
+        running_containers=$(docker ps -q)
+        if [ -n "$running_containers" ]; then
+          docker stop $running_containers
+        fi
+      register: stop_containers_result
+      changed_when: stop_containers_result.stdout != ""
+
+    - name: Remove all stopped Docker containers
+      ansible.builtin.command: docker container prune -f
+      register: prune_containers_result
+      changed_when: "'Deleted Containers:' in prune_containers_result.stdout"