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

kubernetes/manifests/configmap.yaml

@@ -13,4 +13,5 @@ data:
   MAX_COUNTER: "10"
   CANARY_TOKEN_TRIES: "10"
   PROBABILITY_ERROR_CODES: "0"
+  SERVER_HEADER: "Apache/2.2.22 (Ubuntu)"
 #  CANARY_TOKEN_URL: set-your-canary-token-url-here