Allow admins to set failure modes on stages

If a stage fails, such as a source or webauthn stage, allow admin to set what happens. For example, if a source stage fails, redirect the user to another flow/stage.

Linked to https://github.com/goauthentik/authentik/issues/23898

Start by reading linked issue #23898 to understand the related flow and stage requirements. Identify where stage failures are handled and where administrators configure flows; done should allow an administrator to choose failure behavior, including redirecting from a failed stage to another flow or stage.

Written by the indexing model from the issue text.