Hide operation parameters from OpenAPI schema

[Shadow53]

Description of the feature

I'm using the RequestId middleware with poem_openapi. Every operation takes a custom RequestId type as an argument (which extracts the header added by the middleware) for use in the operation itself. Since the header is added by middleware, I don't want it to appear in the generate OpenAPI spec. A #[oai(hidden)] attribute would be a nice parallel with the same attribute on the operation.

Code example (if possible)

#[OpenAPI]
impl Api {
    #[oai(...)]
    async fn operation(
        &self,
        #[oai(hidden)] request_id: RequestId,  // This
        ...,
    ) -> Result<()> {
        todo!()
    }
}