http: add maxHeaderSize property

This commit exposes the value of --max-http-header-size
as a property of the http module.

PR-URL: https://github.com/nodejs/node/pull/24860
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Shelley Vohr <codebytere@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-http-max-header-size.js

@@ -0,0 +1,11 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+const { spawnSync } = require('child_process');
+const http = require('http');
+
+assert.strictEqual(http.maxHeaderSize, 8 * 1024);
+const child = spawnSync(process.execPath, ['--max-http-header-size=10', '-p',
+                                           'http.maxHeaderSize']);
+assert.strictEqual(+child.stdout.toString().trim(), 10);