mgr/dashboard: Use onCancel on any modal event

mgr/dashboard: Use onCancel on any modal event

The problem was, that if 'onCancel' was provided, it wasn't used in all
modal exit cases. Only for the close buttons (the X and the labeled
one), but not if you clicked outside the modal or hit escape.

'onCancel' is currently only used inside the user management form, where
the problem caused, that the submit button was not longer click able if
the modal was hidden through clicking outside of it or hitting escape.

Fixes: https://tracker.ceph.com/issues/40828
Signed-off-by: Stephan Müller <smueller@suse.com>