Remove Python app example and replace with header-echo server for testing

- Deleted the `/examples/docker/python-app` directory and associated files.
- Integrated a custom `header-echo` server for Kubernetes and Docker Compose tests.
- Updated Kubernetes and Docker Compose configurations to use the new `header-echo-server:test` image.
- Enhanced Kubernetes integration tests to validate JSON responses and Cloudflare IP translation behavior.

examples/fixtures/header-echo/server.py

@@ -0,0 +1,33 @@
+#!/usr/bin/env python3
+"""Simple HTTP server that echoes all request headers"""
+
+from http.server import HTTPServer, BaseHTTPRequestHandler
+import json
+
+class HeaderEchoHandler(BaseHTTPRequestHandler):
+    def do_GET(self):
+        self.send_response(200)
+        self.send_header('Content-Type', 'application/json')
+        self.end_headers()
+
+        # Collect all headers
+        headers = dict(self.headers)
+
+        # Add the client IP as seen by this server
+        response = {
+            'headers': headers,
+            'client_ip': self.client_address[0],
+            'x_forwarded_for': self.headers.get('X-Forwarded-For', 'NOT SET')
+        }
+
+        self.wfile.write(json.dumps(response, indent=2).encode())
+
+    def log_message(self, format, *args):
+        # Log to stdout
+        print(f"{self.address_string()} - {format % args}")
+
+if __name__ == '__main__':
+    port = 8080
+    server = HTTPServer(('0.0.0.0', port), HeaderEchoHandler)
+    print(f'Header echo server running on port {port}...')
+    server.serve_forever()