docs: document sendExtraMessageFields

Author: MaxLeiter

docs/pages/docs/api-reference/use-chat.mdx

@@ -105,6 +105,11 @@ Options passed to `useChat`:
       'credentials',
       '"omit" | "same-origin" | "include"',
       'An optional literal that sets the mode of credentials to be used on the request. Defaults to "same-origin".'
+    ],
+    [
+      'sendExtraMessageFields',
+      'boolean',
+      'An optional boolean that determines whether to send extra fields you\'ve added to `messages`. Defaults to `false` and only the `content` and `role` fields will be sent to the API endpoint.'
     ]
   ]}
 />

docs/pages/docs/api-reference/use-completion.mdx

@@ -147,6 +147,11 @@ export default function Completion() {
       'credentials',
       '"omit" | "same-origin" | "include"',
       'An optional literal that sets the mode of credentials to be used on the request. Defaults to "same-origin".'
+    ],
+    [
+      'sendExtraMessageFields',
+      'boolean',
+      "An optional boolean that determines whether to send extra fields you've added to `messages`. Defaults to `false` and only the `content` and `role` fields will be sent to the API endpoint."
     ]
   ]}
 />