k8s: add alert listing/query and filter primitives

Add PrometheusAlerts implementation with:
- Alert fetching from platform and user-workload Prometheus/Thanos
- Rule group fetching with namespace-scoped Thanos tenancy queries
- State-based filtering (firing, pending, silenced)
- Label-based flat filtering with key=value matching
- TLS transport with service CA for in-cluster communication

Signed-off-by: avlitman <alitman@redhat.com>
Signed-off-by: Shirly Radco <sradco@redhat.com>
Signed-off-by: machadovilaca <machadovilaca@gmail.com>
Co-authored-by: Cursor AI Agent <cursor-ai@users.noreply.github.com>
Made-with: Cursor

Author: sradco

pkg/k8s/const.go

@@ -2,4 +2,33 @@ package k8s
 
 const (
 	ClusterMonitoringNamespace = "openshift-monitoring"
+
+	PlatformRouteNamespace            = "openshift-monitoring"
+	PlatformRouteName                 = "prometheus-k8s"
+	PlatformAlertmanagerRouteName     = "alertmanager-main"
+	UserWorkloadRouteNamespace        = "openshift-user-workload-monitoring"
+	UserWorkloadRouteName             = "prometheus-user-workload"
+	UserWorkloadAlertmanagerRouteName = "alertmanager-user-workload"
+	PrometheusAlertsPath              = "/v1/alerts"
+	PrometheusRulesPath               = "/v1/rules"
+	AlertmanagerAlertsPath            = "/api/v2/alerts"
+	UserWorkloadAlertmanagerPort      = 9095
+	UserWorkloadPrometheusServiceName = "prometheus-user-workload-web"
+	UserWorkloadPrometheusPort        = 9090
+
+	ThanosQuerierNamespace               = "openshift-monitoring"
+	ThanosQuerierServiceName             = "thanos-querier"
+	ThanosQuerierTenancyRulesPortName    = "tenancy-rules"
+	DefaultThanosQuerierTenancyRulesPort = 9093
+	ThanosQuerierTenancyAlertsPath       = "/api/v1/alerts"
+	ThanosQuerierTenancyRulesPath        = "/api/v1/rules"
+	ServiceCAPath                        = "/var/run/secrets/kubernetes.io/serviceaccount/service-ca.crt"
+
+	AlertSourceLabel    = "openshift_io_alert_source"
+	AlertSourcePlatform = "platform"
+	AlertSourceUser     = "user"
+	AlertBackendLabel   = "openshift_io_alert_backend"
+	AlertBackendAM      = "alertmanager"
+	AlertBackendProm    = "prometheus"
+	AlertBackendThanos  = "thanos"
 )