Feature: support extensions in `utoipa::IntoParams` attribute macros

[aybeshlikyan]

Hello, this is a great project!!
I saw the MR that added support for extensions on the path macro and param tuples: #1292

I'm hoping to extend (pun intended) the support further to be able to specify extensions(...) as part of the #[into_params] and #[params] attribute macros as well, like this:

#[derive(Debug, Clone, utoipa::IntoParams)]
#[into_params(parameter_in = Query, extensions(("x-on-all-params" = json!(true))))]
pub struct ParamStruct {
    /// A param.
    pub param_1: i32,

    /// Another param.
    #[param(extensions(("x-on-one-param" = json!({ "key": "value" }))))]
    pub param_2: String,
}

I have the changes working on a local branch and would love to put it up for review!