feat: document external redirects (#10704)

Co-authored-by: Sarah Rainsberger <[email protected]>
Co-authored-by: sarahrainsberger <[email protected]>

Author: ematipico

src/content/docs/en/guides/routing.mdx

@@ -250,14 +250,17 @@ You can define rules to [redirect users to permanently-moved pages](#configured-
 
 <p><Since v="2.9.0" /></p>
 
-You can specify a mapping of permanent redirects in your Astro config with the `redirects` value. For most redirects, this is a mapping of an old route to the new route:
+You can specify a mapping of permanent redirects in your Astro config with the [`redirects`](/en/reference/configuration-reference/#redirects) value.
+
+For internal redirects, this is a mapping of an old route path to the new route. As of Astro v5.2.0, it is also possible to redirect to external URLs that start with `https` or `https` and [can be parsed](https://developer.mozilla.org/en-US/docs/Web/API/URL/canParse_static):
 
 ```js title="astro.config.mjs" {4-6}
 import { defineConfig } from 'astro/config';
 
 export default defineConfig({
   redirects: {
-    '/old-page': '/new-page'
+    '/old-page': '/new-page',
+    '/blog': "https://example.com/blog"
   }
 });
 ```
@@ -282,6 +285,10 @@ export default defineConfig({
     '/old-page': {
       status: 302,
       destination: '/new-page'
+    },
+    '/news': {
+      status: 302,
+      destination: "https://example.com/news"
     }
   }
 });