Feat/prometheus-exporter : Add prometheus exporter and grafana dashboard for mailcow. (#6314)

* add : readme for prometheus exporter configs

* add : grafana dashboard json file

* add: prometheus exporter service on docker-compose.override.yml

* migrate: doc files into docs.mailcow.email project

* add : security configs in prometheus exporter compose file

* add : explain more in my comment part in prometheus override compose file

* remove : mailcow dockerized docs

---------

Co-authored-by: Saji <saji@abrnoc>

helper-scripts/docker-compose.override.yml.d/PROMETHEUS_EXPORTER/docker-compose.override.yml

@@ -0,0 +1,18 @@
+services:
+    prometheus-exporter-mailcow:
+      image: ghcr.io/mailcow/prometheus-exporter:2
+      ports:
+        - "9099:9099"
+      restart: always
+      environment:
+        MAILCOW_EXPORTER_HOST: "<your-mail-domain>" # Replace with your Mailcow hostname
+        MAILCOW_EXPORTER_API_KEY: "<your-API-Key>" # Replace with your API key
+        MAILCOW_EXPORTER_TOKEN: "<your-secure-token>" # Replace with your secure key
+        # MAILCOW_EXPORTER_TOKEN_DISABLE: "true" # Uncomment only if it is safe to disable token authentication (e.g., internal network only)
+      dns:
+        - ${IPV4_NETWORK:-172.22.1}.254
+      networks:
+        mailcow-network:
+          ipv4_address: ${IPV4_NETWORK:-172.22.1}.209
+          aliases:
+            - prometheus-exporter