docs: Update doc string for `server_names` (#23629)

Signed-off-by: Arko Dasgupta <arko@tetrate.io>

Mirrored from https://github.com/envoyproxy/envoy @ 4a16086bbd956f6adf93880f33634f38fcdbe3c1

envoy/config/listener/v3/listener_components.proto

@@ -155,6 +155,7 @@ message FilterChainMatch {
   // will be first matched against ``www.example.com``, then ``*.example.com``, then ``*.com``.
   //
   // Note that partial wildcards are not supported, and values like ``*w.example.com`` are invalid.
+  // The value ``*`` is also not supported, and ``server_names`` should be omitted instead.
   //
   // .. attention::
   //