actix-session: Partitioned parameter

Browsers are beginning to block 3rd party cookies, using `Partitioned` is a way to allow per-site 3rd party cookies, for example for logins.

See: https://developer.mozilla.org/en-US/docs/Web/Privacy/Privacy_sandbox/Partitioned_cookies

Would be nice to have a `cookie_partitioned(bool)` similar to how `cookie_secure` behaves, to set the attribute.