Add support for setting no_external_auth in libopenconnect
Add a new function to libopenconnect which will be able to set the no_external_auth
option from struct openconnect_info
.
This feature is required for allowing this configuration option to be set by NetworkManager-openconnect. It will allow to fix the issue: https://gitlab.gnome.org/GNOME/NetworkManager-openconnect/-/issues/116