NavTree: Group APM and Infra plugins under "Observability" section (#104192)

* put o11y department apps under Observability menu section

* fix tests

* change url for observability grouping

* add routing for /observability

pkg/services/navtree/models.go

@@ -21,7 +21,7 @@ const (
 	WeightAlertsAndIncidents
 	WeightAIAndML
 	WeightTestingAndSynthetics
-	WeightMonitoring
+	WeightObservability
 	WeightCloudServiceProviders
 	WeightInfrastructure
 	WeightApplication
@@ -44,7 +44,7 @@ const (
 	NavIDAlertsAndIncidents   = "alerts-and-incidents"
 	NavIDTestingAndSynthetics = "testing-and-synthetics"
 	NavIDAlerting             = "alerting"
-	NavIDMonitoring           = "monitoring"
+	NavIDObservability        = "observability"
 	NavIDInfrastructure       = "infrastructure"
 	NavIDFrontend             = "frontend"
 	NavIDReporting            = "reports"