doc: mark settings as optional and add callback

The settings are currently not required and the callback was not
documented so far.

Refs: #26811

PR-URL: #26894
Refs: #26811
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/api/http2.md

@@ -572,12 +572,17 @@ Provides miscellaneous information about the current state of the
 
 An object describing the current status of this `Http2Session`.
 
-#### http2session.settings(settings)
+#### http2session.settings([settings][, callback])
 <!-- YAML
 added: v8.4.0
 -->
 
 * `settings` {HTTP/2 Settings Object}
+* `callback` {Function} Callback that is called once the session is connected or
+  right away if the session is already connected.
+  * `err` {Error|null}
+  * `settings` {HTTP/2 Settings Object} The updated `settings` object.
+  * `duration` {integer}
 
 Updates the current local settings for this `Http2Session` and sends a new
 `SETTINGS` frame to the connected HTTP/2 peer.
@@ -2232,7 +2237,7 @@ Returns an object containing the default settings for an `Http2Session`
 instance. This method returns a new object instance every time it is called
 so instances returned may be safely modified for use.
 
-### http2.getPackedSettings(settings)
+### http2.getPackedSettings([settings])
 <!-- YAML
 added: v8.4.0
 -->