Add protocol support and improve FastCGI plugin handling

- Introduced `easyhaproxy.proto` annotation for backend protocol configuration.
- Automatically set FastCGI protocol (`proto: fcgi`) when using the FastCGI plugin.
- Updated Kubernetes processor to handle `proto` annotations.
- Enhanced EasyMapping to allow plugin overrides for host-level configs.
- Updated documentation to reflect new `proto` behavior and FastCGI improvements.
- Improved multiprocessing configuration with better context handling in `haproxy.py`.

tests_e2e/docker/docker-compose-php-fpm.yml

@@ -77,9 +77,9 @@ services:
       easyhaproxy.http.port: 80
       # PHP-FPM listens on port 9000
       easyhaproxy.http.localport: 9000
-      easyhaproxy.http.proto: fcgi
 
       # Enable FastCGI plugin for PHP environment configuration
+      # Note: proto fcgi is set automatically by the fastcgi plugin
       easyhaproxy.http.plugins: fastcgi
 
       # FastCGI plugin configuration