Embedding clarification for subroutes.

Can embed grpcui in a server and its working great via

```go
target := "localhost:4321"
cc, err := grpc.DialContext(ctx, target, grpc.WithBlock(), grpc.WithTransportCredentials(insecure.NewCredentials()))
if err != nil {
return err
}
h, err := standalone.HandlerViaReflection(ctx, cc, target)
if err != nil {
return err
}
router.Mount("/", h)
```

However I have want to mount to `router.Mount("/ui", h)`. That doesn't work and I'm wondering if its even possible or is there parts that expect to be absolute to the root path. Any guidance would be wonderful.