refs #21045 add app config to disable unlimited quota and to set max quota

avoid unlimited quota as default_quota fallback value if unlimited quota is not allowed
avoid getting/setting/displaying unlimited default quota if not allowed
implement tests for unlimited quota restrictions

Signed-off-by: Julien Veyssier <eneiluj@posteo.net>
Signed-off-by: npmbuildbot-nextcloud[bot] <npmbuildbot-nextcloud[bot]@users.noreply.github.com>