[fix] redirect logout

[zamentur]

Problem

Logout on sso was broken and don't return on the nextcloud login form.

Solution

Fix all the things and logout on sso only if it's a ldap user (it's possible to create internal nextcloud user side to the ldap users...)

PR Status

• [x] Code finished and ready to be reviewed/tested
• [x] The fix/enhancement were manually tested (if applicable)

Automatic tests

Automatic tests can be triggered on https://ci-apps-dev.yunohost.org/ after creating the PR, by commenting "!testme", "!gogogadgetoci" or "By the power of systemd, I invoke The Great App CI to test this Pull Request!". (N.B. : for this to work you need to be a member of the Yunohost-Apps organization)