Methods are added to NetworkManager::SecretAgent to allow passing a capabilities argument. This is intended for plasma-nm to pass flag NM_SECRET_AGENT_CAPABILITY_VPN_HINTS in the registration process. Later, changes will have to be made to plasma-nm and the VPN plugins to use this new methods and pass hints from SecretAgent::GetSecrets() to VPN plugins.
Partial development so solve https://bugs.kde.org/show_bug.cgi?id=424678