Improve user flow when logging in

[wotwot563]

Is your feature request related to a problem? Please describe.
When the user clicks on the login button, they click on the 'FHICT' button, then get redirected to the backend Identity server, where they have to click "Fontys" again. This is quite confusing for the end-user.

Describe the solution you'd like
Upon clicking "Login with FHICT" in the frontend, automatically redirect them through the identity server to the Fontys identity server.
This way the user does not see the unstyled IdentityServer, this will improve usability.

It would be preferred if we could make a general way of handling this so we can easily add "Login with Surfcontext" in the future, without having the user going to our Identity server again. Making a re-usable implementation of this streamlines the future login implementations.

Additional context
Some people will still need to login with the "local login" in the identity server, we will probably need a new button for this on the frontend "Login with Identity Server" and a flow that does not redirect them through our Identity Server but that uses the old flow.

This issue will require changes in both the backend and in the frontend.