http: send connection: close when closing conn

HTTP/1.1 mandates connections which do not support keep-alive and
close the connection send the connection: close header, see
https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.10

This page also provides more information:
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Connection

I understand that HTTP/1.1 defaults to keep-alive - and that the
Connection: close header is required when closing a connection.

This adds the Connection: close header in the 400 and 414
responses sent on client errors.

PR-URL: https://github.com/nodejs/node/pull/26467
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

test/parallel/test-http-header-overflow.js

@@ -39,7 +39,8 @@ server.listen(0, mustCall(() => {
   c.on('end', mustCall(() => {
     assert.strictEqual(
       received,
-      'HTTP/1.1 431 Request Header Fields Too Large\r\n\r\n'
+      'HTTP/1.1 431 Request Header Fields Too Large\r\n' +
+      'Connection: close\r\n\r\n'
     );
     c.end();
   }));