Add support for OpenID Connect authorization method

OpenID Connect is a layer that is on top of OAuth2 and requires a small addition to the API to make it possible. Currently Qt supports using client_secret_post which puts the client secret into the request body. OpenID Connect also has support for client_secret_basic which puts it in the request headers instead.

What would be good to add here is a function that enables the user to specify the type of authentication (client_secret_[post|basic]) and then QtNetworkAuth can handle the correct way of passing that forward.