Add `SameSite` enum support to `ResponseCookie`

[zinzoddari]

I have added the SameSite enum to ResponseCookie while ensuring that the existing string-based handling is still supported.

The reason for adding the enum is to enhance type safety. Additionally, if a value that is not provided is entered, it will default to Lax as per the specification (https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-rfc6265bis#name-the-samesite-attribute).

I would appreciate it if you could review the PR!