feat(middleware): add HostFilterLater::disable

[niklasad1]

This is just a convenience method to make it easier to use in some scenarios because when enabled it will generate another type

Such as this example won't compile:

   let middleware = if host_filter {
       tower::ServiceBuilder::new()
           .layer(HostFilterLayer::new(["example.com"]).unwrap())
           .layer(ProxyGetRequestLayer::new("/health", "system_health").unwrap())
   } else {
       tower::ServiceBuilder::new()
   };

[lexnv]

LGTM!

[jsdw]

Maybe an argument for not exposing the ServiceBuilder stuff at all and accepting layers instead or something, but yup lgtm :)