mgr/dashboard: fix access control permissions for roles

mgr/dashboard: fix access control permissions for roles

Since prometheus is being used in the dashboard page we need to make
sure every role has prometheus read only access so that the dashboard
page can load the utilization metrics.

I also saw permission issue with the osd settings endpoint when its
trying to get the nearfull/full ratio. so instead of failing the entire
page i am proceeding with a chart that doesn't have those details when
the user doesn't have permission to access the config opt.

Multisite page was not accessible in the case of rgw-manager or
read-only user because its trying to show the status of rgw module. This
si also now gracefully handled to show the alert only when the user has
sufficient permission.

Fixes: https://tracker.ceph.com/issues/70331
Signed-off-by: Nizamudeen A <nia@redhat.com>