feat: Add IP_RANGES_FETCH_ENABLED environment variable

This change adds a new environment variable to control whether IP ranges
are fetched during application startup. When set to 'false', the initial
fetch will be skipped, which can:

1. Speed up application startup
2. Avoid connectivity issues in environments with restricted internet access
3. Prevent startup failures when CloudFront or CloudFlare services are unreachable

docs/src/advanced-config/index.md

@@ -161,6 +161,14 @@ The easy fix is to add a Docker environment variable to the Nginx Proxy Manager
       DISABLE_IPV6: 'true'
 ```
 
+## Disabling IP Ranges Fetch
+
+By default, NPM fetches IP ranges from CloudFront and Cloudflare during application startup. In environments with limited internet access or to speed up container startup, this fetch can be disabled:
+
+```yml
+    environment:
+      IP_RANGES_FETCH_ENABLED: 'false'
+```
 
 ## Custom Nginx Configurations