[server] Set SameSite option on cookie
[server] Set SameSite option on cookie

Summary: Context on this new option [here](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Set-Cookie/SameSite). Firefox was complaining when I was testing my local instance that non-https cookies will soon not work unless they have `SameSite` set.

Reviewers: palys-swm

Reviewed By: palys-swm

Subscribers: KatPo, zrebcu411, Adrian

Differential Revision: https://phabricator.ashoat.com/D102

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