support partitioned CHIPS cookies

[gregwebs]

Chrome warns about cross-domain cookies.

Cookie set in cross-site context will be blocked in future Chrome versions
In a future version of the browser, cookies marked with SameSite=None; Secure and not Partitioned will be blocked in cross-site context. This behavior protects user data from cross-site tracking.

The go standard library doesn't yet support this, but in the end a cookie is just a simple header that SCS could append to.

[alexedwards]

I'd be happy to add this, but I'm wary of changing the public API of the SessionCookie type until we know exactly what the implementation will look like in net/http. Let's keep this issue open, but label it as blocked for now.

[papidb]

Hi @alexedwards is there a way to set this using the library?