Extracting out `&str` from `mongodb::error::ErrorKind::Custom()`

[sumit-modak]

This is a feature request.

    if let Err(e) = crate::database::check_and_add_user(state.as_ref(), &user).await {
        // `e` is of type mongodb::error::Error
        match e.kind.as_ref() {
            mongodb::error::ErrorKind::Custom(s) => {
                // `s` is of type &Arc<dyn Any + Send + Sync>
                return Err((
                    StatusCode::BAD_REQUEST,
                    // implement here
                    // <-- how to convert s to &str or String
                ));
            }
            _ => {
                return Err((
                    StatusCode::INTERNAL_SERVER_ERROR,
                    format!("Failed to create user"),
                ))
            }
        };
    }
    ```

[sumit-modak]

            if let Err(e) = crate::database::check_and_add_user(state.as_ref(), &user).await {
                eprintln!("{e}");
                if let Some(s) = e.get_custom::<&str>() {
                    return Err((StatusCode::BAD_REQUEST, s.to_string()));
                } else {
                    return Err((
                        StatusCode::INTERNAL_SERVER_ERROR,
                        format!("Failed to create user"),
                    ));
                }
            }

This is the right way of doing it...