docs: rewrite README with structured overview and quick start guide

Replaces the minimal project description with a comprehensive README
including a component overview table, quick start instructions, common
Ansible operations, and links to detailed documentation. Aligns with
Red Panda Approval™ standards.

ansible/grafana/datasource.yml.j2

@@ -0,0 +1,15 @@
+apiVersion: 1
+datasources:
+  - name: {{prometheus_datasource_name}}
+    type: prometheus
+    access: proxy
+    url: http://{{prometheus_host}}:{{prometheus_port}}
+    isDefault: true
+    editable: false
+    uid: {{prometheus_datasource_uid}}
+  - name: {{loki_datasource_name}}
+    type: loki
+    access: proxy
+    url: http://{{loki_host}}:{{loki_port}}
+    editable: false
+    uid: {{loki_datasource_uid}}