bump SystemMemoryExceedsReservation alert threshold to 95%

In order to reduce the excessive firing of this alert we
are making it fire at 95% of system memory utilization
instead of the current 90 %. By making this change, we
hope to keep this alert still relevant for users while
reducing the noise.

Signed-off-by: Harshal Patil <harpatil@redhat.com>

install/0000_90_machine-config-operator_01_prometheus-rules.yaml

@@ -51,7 +51,7 @@ spec:
       rules:
         - alert: SystemMemoryExceedsReservation
           expr: |
-            sum by (node) (container_memory_rss{id="/system.slice"}) > ((sum by (node) (kube_node_status_capacity{resource="memory"} - kube_node_status_allocatable{resource="memory"})) * 0.9)
+            sum by (node) (container_memory_rss{id="/system.slice"}) > ((sum by (node) (kube_node_status_capacity{resource="memory"} - kube_node_status_allocatable{resource="memory"})) * 0.95)
           for: 15m
           labels:
             severity: warning