Add built-in plugin framework and initial plugins

- Introduced a plugin system enabling EasyHAProxy extensions.
- Added `CleanupPlugin` (GLOBAL): Handles temporary file cleanup.
- Added `CloudflarePlugin` (DOMAIN): Restores visitor IP from Cloudflare headers.
- Added `DenyPagesPlugin` (DOMAIN): Blocks access to specified paths.
- Documented the plugin architecture, configuration options, and built-in plugins in `docs/plugin-development.md` and `docs/plugins.md`.

src/plugins/builtin/cloudflare.py

@@ -0,0 +1,89 @@
+"""
+Cloudflare Plugin for EasyHAProxy
+
+This plugin restores the original visitor IP address from Cloudflare's
+CF-Connecting-IP header when requests come through Cloudflare's CDN.
+
+Configuration:
+    - ip_list_path: Path to file containing Cloudflare IP ranges (default: /etc/haproxy/cloudflare_ips.lst)
+
+Example YAML config:
+    plugins:
+      cloudflare:
+        enabled: true
+        ip_list_path: /etc/haproxy/cloudflare_ips.lst
+
+Example Container Label:
+    easyhaproxy.http.plugins: "cloudflare"
+
+HAProxy Config Generated:
+    # Cloudflare - Restore original visitor IP
+    acl from_cloudflare src -f /etc/haproxy/cloudflare_ips.lst
+    http-request set-header X-Forwarded-For %[req.hdr(CF-Connecting-IP)] if from_cloudflare
+"""
+
+import os
+import sys
+
+# Add parent directory to path for imports
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from plugins import PluginInterface, PluginType, PluginContext, PluginResult
+
+
+class CloudflarePlugin(PluginInterface):
+    """Plugin to restore original visitor IP from Cloudflare"""
+
+    def __init__(self):
+        self.ip_list_path = "/etc/haproxy/cloudflare_ips.lst"
+        self.enabled = True
+
+    @property
+    def name(self) -> str:
+        return "cloudflare"
+
+    @property
+    def plugin_type(self) -> PluginType:
+        return PluginType.DOMAIN
+
+    def configure(self, config: dict) -> None:
+        """
+        Configure the plugin
+
+        Args:
+            config: Dictionary with configuration options
+                - ip_list_path: Path to Cloudflare IP list file
+                - enabled: Whether plugin is enabled
+        """
+        if "ip_list_path" in config:
+            self.ip_list_path = config["ip_list_path"]
+
+        if "enabled" in config:
+            self.enabled = str(config["enabled"]).lower() in ["true", "1", "yes"]
+
+    def process(self, context: PluginContext) -> PluginResult:
+        """
+        Generate HAProxy config to restore original IP from Cloudflare
+
+        Args:
+            context: Plugin execution context with domain information
+
+        Returns:
+            PluginResult with HAProxy configuration snippet
+        """
+        if not self.enabled:
+            return PluginResult()
+
+        # Generate HAProxy config snippet
+        haproxy_config = f"""# Cloudflare - Restore original visitor IP
+    acl from_cloudflare src -f {self.ip_list_path}
+    http-request set-header X-Forwarded-For %[req.hdr(CF-Connecting-IP)] if from_cloudflare"""
+
+        return PluginResult(
+            haproxy_config=haproxy_config,
+            modified_easymapping=None,
+            metadata={
+                "domain": context.domain,
+                "ip_list_path": self.ip_list_path
+            }
+        )