Frontend - Second authenticator

We need a second button on the Login website, above the "Sign In" Button.

If there's this value:

{{custom_config.get("workshop", {}).get("login", {}).get("enabled", False)}}

we have to make the second Login Button visible.

Text for the new login Button: "Workshop Sign In" Text for the regular sign in button: "Regular Sign In".

Additionally: If both of the following is true, we will hide the regular sign in button:

• the next argument in the URL starts with "%2Fhub%2Fworkshop" ( e.g. https://jupyter.jsc.fz-juelich.de/hub/login?next=%2Fhub%2Fworkshops/whatever)
• workshop.login.enbaled is true in customConfig.