Fix cookie setup

[anjackson]

We are seeing this warning:

Cookie “PLAY_SESSION” will be soon rejected because it has the “SameSite” attribute set to “None” or an invalid value, without the “secure” attribute. To know more about the “SameSite“ attribute, read https://developer.mozilla.org/docs/Web/HTTP/Headers/Set-Cookie/SameSite

Would be good to bring this into line with

ukwa/ukwa-services@d0099fb

e.g. Path=/act; SameSite=Strict; HttpOnly; Secure; Priority=High;

See the docs on configuration options: https://www.playframework.com/documentation/2.6.x/SettingsSession