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/templates/grafana-stack/config/alertmanager/alertmanager.yml.j2

@@ -0,0 +1,18 @@
+global:
+  resolve_timeout: 5m
+
+route:
+  receiver: default
+  group_by: [alertname, instance]
+  group_wait: 30s
+  group_interval: 5m
+  repeat_interval: 4h
+
+receivers:
+  - name: default
+{% if alertmanager_webhook_url | length > 0 %}
+    webhook_configs:
+      - url: "{{ alertmanager_webhook_url }}"
+        send_resolved: true
+{% endif %}
+