Add FastCGI Plugin for PHP-FPM support with examples, tests, and documentation

- Introduced `FastcgiPlugin` for automatic HAProxy `fcgi-app` configuration generation.
- Added example Docker Compose setup for PHP-FPM with FastCGI.
- Updated documentation with detailed examples and usage instructions for FastCGI.
- Included test cases to validate plugin behavior and generated configurations.
- Enhanced `easymapping` to support `fcgi-app` definitions in global configs.

examples/docker/php-app/info.php

@@ -0,0 +1,9 @@
+<?php
+/**
+ * PHP Info Page
+ *
+ * This page displays comprehensive PHP configuration information
+ * including FastCGI environment variables set by EasyHAProxy.
+ */
+
+phpinfo();