- Introduced `IpWhitelistPlugin` (DOMAIN): Restricts access to specific IP addresses or CIDR ranges.
- Added configuration options: `enabled`, `allowed_ips`, and `status_code`.
- Updated `plugins.md` and `plugin-development.md` to document `IpWhitelistPlugin`.
- Created fixtures for `services-with-ip-whitelist`.
- Added extensive test cases for `IpWhitelistPlugin` to validate configuration and HAProxy output generation.
- Ensured seamless integration into the plugin framework alongside other domain plugins.
