http: fix capitalization of 418 status message

Update the message to be consistent with RFC 7168. Add a note to
"Multiple Choices" regarding RFC 7231 superseding RFC 7168.

PR-URL: https://github.com/nodejs/node/pull/20700
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Yuta Hiroto <hello@hiroppy.me>t

Co-authored-by: Antoine du Hamel <duhamelantoine1995@gmail.com>

lib/_http_server.js

@@ -67,7 +67,7 @@ const STATUS_CODES = {
   207: 'Multi-Status',               // RFC 4918
   208: 'Already Reported',
   226: 'IM Used',
-  300: 'Multiple Choices',
+  300: 'Multiple Choices',           // RFC 7231
   301: 'Moved Permanently',
   302: 'Found',
   303: 'See Other',
@@ -93,7 +93,7 @@ const STATUS_CODES = {
   415: 'Unsupported Media Type',
   416: 'Range Not Satisfiable',
   417: 'Expectation Failed',
-  418: 'I\'m a teapot',              // RFC 2324
+  418: 'I\'m a Teapot',              // RFC 7168
   421: 'Misdirected Request',
   422: 'Unprocessable Entity',       // RFC 4918
   423: 'Locked',                     // RFC 4918