* Deprecate `sso_immediate_redirect` and add welcome-page only option
The old `sso_immediate_redirect` option is kept in code for backwards compatibility, but is replaced by `sso_redirect_options.immediate`, where a new `on_welcome_page` option is also introduced to only target entry points to the app.
The path matching is a bit brittle, but still ideal in the sense of not showing UI while the app realizes it needs to redirect.
The new welcome page-only option is fully intended to avoid breaking permalinks and such while still redirecting when needed. In future, other options might be added here to further tune the experience.
* Add note about guests