[stable/2024.1] fix: nova capacity alert (#1593)

This is an automated cherry-pick of #1306
/assign mnaser

roles/kube_prometheus_stack/files/jsonnet/openstack.libsonnet

@@ -259,7 +259,7 @@
               description: 'The cloud capacity is currently at `{{ $value }}` which means there is a risk of running out of capacity due to the timeline required to add new nodes. Please ensure that adequate amount of infrastructure is assigned to this deployment to prevent this.',
               summary: '[nova] Capacity risk',
             },
-            expr: 'sum (     openstack_nova_memory_used_bytes   + on(hostname) group_left(adminState)     (0 * openstack_nova_agent_state{exported_service="nova-compute",adminState="enabled"}) ) / sum (     openstack_nova_memory_available_bytes   + on(hostname) group_left(adminState)     (0 * openstack_nova_agent_state{exported_service="nova-compute",adminState="enabled"}) ) * 100 > 75',
+            expr: 'sum (     openstack_nova_memory_used_bytes   + on(hostname) group_left(adminState)     (0 * openstack_nova_agent_state{exported_service="nova-compute",adminState="enabled"}) ) / sum (     openstack_nova_memory_available_bytes*0.90   + on(hostname) group_left(adminState)     (0 * openstack_nova_agent_state{exported_service="nova-compute",adminState="enabled"}) ) * 100 > 75',
             'for': '6h',
             labels: {
               severity: 'warning',