[feature] Add support for `SameSite` attribute in `WSCookie`

[jonaskoelker-jypo]

The SameSite cookie attribute is widespread, see e.g. https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Set-Cookie/SameSite#browser_compatibility.

It would be great if play-ws helped me consume SameSite attributes, e.g. by having a sameSite field on WSCookie.