fix(lb): add match subdomain for routes (#4354)

Author: RoRoJ

pages/load-balancer/how-to/create-manage-routes.mdx

@@ -47,7 +47,9 @@ Routes allow you to specify, for a given frontend, which backends it should dire
 
     - **SNI value**: Enter an SNI value to filter for (for example `www.example-domain.com`). Traffic with a matching SNI value will be directed to the specified target backend.
 
-8. Click **Create route** to finish.
+8. Choose whether to match all subdomains of the given SNI / Host header value, by checking the relevant box. This will ensure that all requests to subdomains of the value (e.g. `blog.example-domain.com`) also use this route.
+
+9. Click **Create route** to finish.
 
   Your route is created, and you are taken to the list of all your routes for this Load Balancer.