mgr/dashboard: Handle errors for /api/osd/settings

mgr/dashboard: Handle errors for /api/osd/settings

Fixes https://tracker.ceph.com/issues/62089

issue:
=====
/api/osd/settings returns "TypeError: string indices must be
integers" sometimes.
The result is coming from `osd dump` command which instead of returning
an object returns an error message which then displays error on
dashboard.

fix:
====
Added a try-catch block to handle error and updated frontend code to
handle those

Signed-off-by: Afreen <afreen23.git@gmail.com>