Add keycloack trusted device error

[WesHarrell]

Add information to login/connection docs to cover keycloak error desribed by Nat in this Slack thread: https://nesi.slack.com/archives/CJUNJ2DKN/p1766027720491799

[natnesi]

thanks Wes, worth to have a troubleshooting section, if this "We are sorry..." Unexpected error when handling authentication request to identity provider" error happens then it is likely that the users try to add a trusted device with the same name of an existing trusted device. Worth reading the page on trusted devices as maybe a trusted device should not be used in that case.