refactor: update Nginx configuration and Docker setup

- Change user directive in Nginx configuration from 'nginx' to 'www-data'.
- Update upstream server configurations in Nginx to use 'localhost' instead of service names.
- Modify Nginx server block to redirect HTTP to a status page instead of Grafana.
- Rename Alertmanager location from '/alertmanager/' to '/alerts/' for consistency.
- Remove deprecated status page configuration and related files.
- Adjust Prometheus configuration to reflect the new Docker network settings.

infra/nginx/conf.d/grafana.conf

@@ -1,6 +1,6 @@
 # Grafana proxy configuration
 location /grafana/ {
-    proxy_pass http://grafana_backend/;
+    proxy_pass http://grafana_backend;
     proxy_set_header Host $host;
     proxy_set_header X-Real-IP $remote_addr;
     proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;