doc: fix http and http2 writeEarlyHints() parameter

Both http and http2 `response.writeEarlyHints()` take an object,
not an array, as their first parameter. For http, this was updated in
the examples via #44820 except for the final example, which this
patch fixes.
The doc for the http2 version was not touched in #44820 although
I am pretty sure from skimming the code that it behaves identically
to http, and so propose to change its doc as well.
Finally, some bogus headline levels are fixed in http2 docs.

PR-URL: #45000
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com>

doc/api/http.md

@@ -2175,7 +2175,9 @@ response.writeEarlyHints({
 });
 
 const earlyHintsCallback = () => console.log('early hints message sent');
-response.writeEarlyHints(earlyHintsLinks, earlyHintsCallback);
+response.writeEarlyHints({
+  'link': earlyHintsLinks,
+}, earlyHintsCallback);
 ```
 
 ### `response.writeHead(statusCode[, statusMessage][, headers])`

doc/api/http2.md

@@ -3787,7 +3787,7 @@ Removes a header that has been queued for implicit sending.
 response.removeHeader('Content-Encoding');
 ```
 
-### `response.req`
+#### `response.req`
 
 <!-- YAML
 added: v15.7.0
@@ -4005,30 +4005,34 @@ Sends a status `100 Continue` to the client, indicating that the request body
 should be sent. See the [`'checkContinue'`][] event on `Http2Server` and
 `Http2SecureServer`.
 
-### `response.writeEarlyHints(links)`
+#### `response.writeEarlyHints(hints)`
 
 <!-- YAML
 added: v18.11.0
 -->
 
-* `links` {string|Array}
+* `hints` {Object}
 
 Sends a status `103 Early Hints` to the client with a Link header,
 indicating that the user agent can preload/preconnect the linked resources.
-The `links` can be a string or an array of strings containing the values
-of the `Link` header.
+The `hints` is an object containing the values of headers to be sent with
+early hints message.
 
 **Example**
 
 ```js
 const earlyHintsLink = '</styles.css>; rel=preload; as=style';
-response.writeEarlyHints(earlyHintsLink);
+response.writeEarlyHints({
+  'link': earlyHintsLink,
+});
 
 const earlyHintsLinks = [
   '</styles.css>; rel=preload; as=style',
   '</scripts.js>; rel=preload; as=script',
 ];
-response.writeEarlyHints(earlyHintsLinks);
+response.writeEarlyHints({
+  'link': earlyHintsLinks,
+});
 ```
 
 #### `response.writeHead(statusCode[, statusMessage][, headers])`