doc: add protocol option in http2.connect()

This option is used here:
https://github.com/nodejs/node/blob/70c32a6d190e2b5d7b9ff9d5b6a459d14e8b7d59/lib/internal/http2/core.js#L3010

PR-URL: #31560
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

doc/api/http2.md

@@ -2257,6 +2257,9 @@ changes:
   * `selectPadding` {Function} When `options.paddingStrategy` is equal to
     `http2.constants.PADDING_STRATEGY_CALLBACK`, provides the callback function
     used to determine the padding. See [Using `options.selectPadding()`][].
+  * `protocol` {string} The protocol to connect with, if not set in the
+    `authority`. Value may be either `'http:'` or `'https:'`. **Default:**
+    `'https:'`
   * `settings` {HTTP/2 Settings Object} The initial settings to send to the
     remote peer upon connection.
   * `createConnection` {Function} An optional callback that receives the `URL`