Returns an owned [`PagesStream`].
In certain situations you can't use streams with borrows. For example, you
can't use a stream with a borrow if a stream should outlive a client in APIs
like this one:
```ignore
fn get_stuff(params: Params) -> impl Stream<Item = Stuff> {
// This client is not needed anywhere else and is cheap to create.
let client = StuffClient::new();
client.pages(GetStuff::from_params(params))
}
```
The client gets dropped after the `.pages` call but the stream we're
returning needs an internal reference to the client in order to perform
the querying. This situation can be fixed by simply using `into_pages` variant
instead:
```ignore
fn get_stuff(params: Params) -> impl Stream<Item = Stuff> {
let client = StuffClient::new(params);
client.into_pages(GetStuff::from_params(params))
}
```
Now the client is consumed into the stream to be used internally.