Configure cookies' "samesite" option

[farshiana]

Hey again,

I think it would be great if we could configure the "samesite" option of cookies. You probably already know it but Flask's set_cookie function allows it.

Thanks!

[vimalloc]

Sure, that seems totally reasonable to me. If you want to submit a PR I would be happy to merge that, or I can throw something together when time allows (likely over the next week or so).

[farshiana]

Thank you, I made a PR. By the way, sorry for not seeing the other issue about this.

[vimalloc]

Released in 3.6.0. Thanks for contributing! 👍