Refactor to schema casting as

[juhaku]

This commit changes the ToSchema trait to be similar with ToResponse trait. It also introduces lifetimes to avoid unnecessary allocations.

pub trait ToSchema<'__s> {
    fn schema() -> (&'__s str, openapi::RefOr<openapi::schema::Schema>);

    fn aliases() -> Vec<(&'__s str, openapi::schema::Schema)> {
        Vec::new()
    }
}

Prior to this commit the name that was used to register a schema to OpenAPI spec was defined in #[openapi(components(schemas(...)))] attribute with syntax like schemas(path::to::Schema as path::MySchema). This is a bit inconvenient at least and behaved completely opposite to how response and request bodies behave when defined in #[utoipa::path] macro.

From now the name of the schema registered in OpenAPI spec will be defined by the ToSchema trait itself the same way as ToResponse does it. It will return a tuple of (name, component) pair.

This also introduces new feature As what is then used to define alternative name for the schema derived from ToSchema if necessary. For example the below struct would be registered to the OpenAPI with name path.to.Foo instead of just Foo when it is added to openapi with #[openapi(components(schemas(Foo)))].

 #[derive(ToSchema)]
 #[schema(as = path::to::Foo)]
 pub struct Foo {
     name: String,
 }