docs: 0 disables route timeout (#7931)

Calling out that it's possible to use the value 0 to disable route timeout (as it is for idle timeout).

Signed-off-by: nmeessen <nmeessen@atlassian.com>

Mirrored from https://github.com/envoyproxy/envoy @ b9fe0b93371094827827b4932aaad09f89b14928

envoy/api/v2/route/route.proto

@@ -562,7 +562,8 @@ message RouteAction {
 
   // Specifies the upstream timeout for the route. If not specified, the default is 15s. This
   // spans between the point at which the entire downstream request (i.e. end-of-stream) has been
-  // processed and when the upstream response has been completely processed.
+  // processed and when the upstream response has been completely processed. A value of 0 will
+  // disable the route's timeout.
   //
   // .. note::
   //