fix(forecastle): Fix absent SLO metric by forcing 0 for absent query

apps/k8s01/forecastle/slo.yaml

@@ -11,8 +11,8 @@ spec:
       description: "forecastle SLO based on availability for HTTP request responses."
       sli:
         events:
-          errorQuery: sum(rate(nginx_ingress_controller_requests{exported_namespace="forecastle",ingress="forecastle",status=~"(5..|429)"}[{{.window}}]))
-          totalQuery: sum(rate(nginx_ingress_controller_requests{exported_namespace="forecastle",ingress="forecastle"}[{{.window}}]))
+          errorQuery: sum(rate(nginx_ingress_controller_requests{exported_namespace="forecastle",ingress="forecastle",status=~"(5..|429)"}[{{.window}}]) or vector(0))
+          totalQuery: sum(rate(nginx_ingress_controller_requests{exported_namespace="forecastle",ingress="forecastle"}[{{.window}}]) or vector(1))
       alerting:
         name: ForecastleHighErrorRate
         labels: