Bugfix: SAML return to same page when session expires.

- Fix config.php $cookie_samesite = "Strict"; handling.

- Use rawurlencode() when setting login redirect headers.

- Cookie SameSite="None" attribute mandates also setting Secure attribute.
  https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Set-Cookie/SameSite
  HTTPS is mandatory when using Cookie SameSite="None", required in some SAML topologies.

- Increase phpipamredirect cookie lifetime to 2 mins.
  2FA authentication may take >10s.

- Add docker COOKIE_SAMESITE env configuration option.

Closes #3429