Add configurable HTTP Server header for deception

Add SERVER_HEADER environment variable to customize the HTTP Server
  response header, defaulting to Apache/2.2.22 (Ubuntu). This allows the
  honeypot to masquerade as different web servers to attract attackers.

  - Add server_header field to Config dataclass
  - Override version_string() in Handler to return configured header
  - Update documentation and all deployment configs

src/handler.py

@@ -46,6 +46,10 @@ class Handler(BaseHTTPRequestHandler):
         """Extract user agent from request"""
         return self.headers.get('User-Agent', '')
 
+    def version_string(self) -> str:
+        """Return custom server version for deception."""
+        return self.config.server_header
+
     def _should_return_error(self) -> bool:
         """Check if we should return an error based on probability"""
         if self.config.probability_error_codes <= 0: