feat: add set_page to Paginator

[dsgallups]

This is a really small QoL change for Paginator. We add a method to set the current page via PaginatorTrait::set_page.

This is useful in where you need to start at a page, and then continue fetch_and_nexting your way to glory.

Currently, you need to something like

let mut paginator = some::Entity::find().paginate(db, page_size);

while paginator.cur_page() < start_at_page {
  paginator.next()
}

And while this is workable, it would be ideal to just start at the page you need:

let mut paginator = some::Entity::find().paginate(db, page_size);
paginator.set_page(start_at_page);

This is quite useful for cases where you need to jump around for different pages up to a point and whatnot. Thanks 🙂

[Huliiiiii]

&mut self -> void or self -> self? @tyt2y3