We should support multiple login options besides password and "Feide" (a NASCAR-menu)

[hmpf]

(I'm struggling to find a good page describing NASCAR menus, websearch is basically FUBARed. It probably has a new, more corporate name now.)

IIRC we already have an AuthMethodListView which allows the frontend to know what login methods are available. We should add one more method temporarily (say, github logins) and verify that the frontend shows all three, and that "Feide" or "Dataporten" is not hardcoded anywhere in the code.

If it works, we document how to do it. If not, we fix it.