Rust Schema type needs ToSchema

[James-Mart]

In order to wrap Events::setSchema (needed to call it inline from Rust services), the Schema type needs to implement ToSchema.

I took a quick look at this and it seemed to get complicated quickly, as it implies that IndexMap and AnyType also both need to implement ToSchema.

[swatanabe]

It won't actually be called, so unimplemented!() will work for now.