mgr/dashboard: Fix for alert notification message being undefined

mgr/dashboard: Fix for alert notification message being undefined

Prometheus alert notification message in the dashboard always comes up
as undefined. Its because we were showing the alert.summary instead of
alert.description for displaying the message. I couldn't find the
summary field in the ceph_default_alerts.yml file. So removed all the
Summary fields from the dashboard code.

Fixes: https://tracker.ceph.com/issues/49342
Signed-off-by: Nizamudeen A <nia@redhat.com>
(cherry picked from commit 2921b2e9a939e1ad52b07327fdf84885568384b9)