Set base_path at runtime?

## Feature Request

It would be great if `base_path` could be set at runtime. People deploy at different sub-paths, and I want to distribute a single binary for all of them.

## Implement Suggestion

I suggest adding an argument to `router` function:

https://github.com/DioxusLabs/dioxus/blob/417bf7a4c17ed86ccf757d6b17abca0bf8a6028d/packages/fullstack-server/src/launch.rs#L96-L104

Like this:

```rust
pub fn router(app: fn() -> Element, base_path: Option) -> Router {
let cfg = ServeConfig::new();
apply_base_path(
Router::new().serve_dioxus_application(cfg.clone(), app),
app,
cfg,
base_path.unwrap_or(base_path().map(|s| s.to_string())),
)
}
```

But this might be too breaking, and impact many people who doesn't need base_path.