feat: hide caldav server settings if no app uses the caldav backend

apps/dav/lib/Settings/CalDAVSettings.php

apps/dav/tests/unit/Settings/CalDAVSettingsTest.php

lib/private/App/AppManager.php

lib/private/App/InfoParser.php

lib/public/App/IAppManager.php

resources/app-info.xsd

tests/data/app/expected-info.json

tests/data/app/navigation-one-item.json

tests/data/app/navigation-two-items.json

tests/data/app/valid-info.xml

tests/lib/App/AppManagerTest.php