RFE: allow openconnect-sso to be spawned from openconnect itself

[dwmw2]

The SAML support has (finally) been merged into OpenConnect in the v9.01 release.

The GNOME NetworkManager auth-dialog has the SSO support merged, and can open a webview natively.
(KDE still needs it implemented: https://bugs.kde.org/show_bug.cgi?id=448153 )

However, we can't do that from openconnect on the command line. I'd love to be able to spawn openconnect-sso to do its qute-browser thing, from openconnect. That way, we can handle all the CSD and other nonsense (cf. #35) and allow openconnect-sso to do what it does best. This would probably allow it to be used for other protocols (cf. #11, #74) more easily too.

[dwmw2]

https://gitlab.com/openconnect/openconnect/-/issues/425