Add observability platform Ansible project

Deploys the Grafana stack (Prometheus/Alertmanager/Loki/Tempo/Grafana with
Alloy as collector) and the ELK stack (Filebeat/Logstash/Elasticsearch/
Kibana) via Docker Compose on a target host. External to the application
repo, pre-built by the mentor.

ansible/roles/observability/handlers/main.yml

@@ -0,0 +1,7 @@
+---
+- name: Restart observability stack
+  community.docker.docker_compose_v2:
+    project_src: "{{ stack_root }}"
+    state: restarted
+  when: stack_root is defined
+