mgr/dashboard: don't log tracebacks on 404s

mgr/dashboard: don't log tracebacks on 404s

Currently we're logging tracebacks on expected request errors as 404,
401, etc. This may cause confusion to users, which might think that
something really wrong was happening there.

This should be extended to many DashboardExceptions that simply return
expected HTTP error codes (403, 415, 3xx, etc).

Fixes: https://tracker.ceph.com/issues/55720
Signed-off-by: Ernesto Puerta <epuertat@redhat.com>