This adds an alert for GitpodWorkspaceHighStartFailureRate (#19099)

Author: mads-hartmann

operations/observability/mixins/workspace/rules/central/workspaces.yaml

@@ -28,6 +28,18 @@ spec:
           gitpod_ws_manager_mk2_workspace_phase_total{type="Regular", phase="Stopping", cluster!~"ephemeral.*"}
         ) without(phase) > 15
 
+    - alert: GitpodWorkspaceHighStartFailureRate
+      labels:
+        severity: critical
+        dedicated: included
+      annotations:
+        runbook_url: https://github.com/gitpod-io/runbooks/blob/main/runbooks/GitpodWorkspaceHighFailureRate.md
+        summary: Workspaces are failing to start in cluster {{ $labels.cluster }}.
+        description: For the last 15 minutes more than 20% of hew workspaces have failed to start
+      for: 15m
+      expr: |
+          sum(increase(gitpod_ws_manager_mk2_workspace_starts_failure_total{type="Regular", cluster!~"ephemeral.*"}[5m])) by (cluster) / sum(increase(gitpod_ws_manager_mk2_workspace_starts_total{type="Regular", cluster!~"ephemeral.*"}[5m])) by (cluster) > 0.2
+
     - alert: GitpodWorkspaceHighFailureRateMk2
       labels:
         severity: critical