Admission webhook for VMAlertmanagerConfig does not handle all invalid configs

[bh-tt]

Applying the following VMAlertmanagerConfig to a cluster with the operator installed and admission webhooks enabled does not result in a failure from the admission webhook but a failure in the operator log. It should result in a validation admission webhook failure.

The failure in this case is a missing require_tls setting in the email_configs.

I'm not sure why the admission webhook would use a different set of validation rules than the actual reconciliation, would that make the validation webhook dependent on other resources present in the cluster?

apiVersion: operator.victoriametrics.com/v1beta1
kind: VMAlertmanagerConfig
metadata:
  name: metric-target-down-test
spec:
  route:
    receiver: email
    group_by: ["service","alertname"]
    routes:
      - receiver: email
        continue: false
  receivers:
    - name: email
      email_configs:
        - to: test@example.com

{"level":"error","ts":1702980403.351607,"logger":"factory","msg":"bad configs found during alertmanager config building","alertmanager":"alertmanager","error":"errors: incorrect email configuration, tls is required, but no config provided at
 spec in object: it/metric-target-down-test, will ignore vmalertmanagerconfig metric-target-down-test","stacktrace":"github.com/VictoriaMetrics/operator/controllers/factory.buildAlertmanagerConfigWithCRDs\n\tgithub.com/VictoriaMetrics/operat
or/controllers/factory/alertmanager.go:657\ngithub.com/VictoriaMetrics/operator/controllers/factory.createDefaultAMConfig\n\tgithub.com/VictoriaMetrics/operator/controllers/factory/alertmanager.go:547\ngithub.com/VictoriaMetrics/operator/con
trollers/factory.CreateOrUpdateAlertManager\n\tgithub.com/VictoriaMetrics/operator/controllers/factory/alertmanager.go:90\ngithub.com/VictoriaMetrics/operator/controllers.(*VMAlertmanagerReconciler).Reconcile\n\tgithub.com/VictoriaMetrics/op
erator/controllers/vmalertmanager_controller.go:86\nsigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Reconcile\n\tsigs.k8s.io/controller-runtime@v0.13.1/pkg/internal/controller/controller.go:121\nsigs.k8s.io/controller-ru
ntime/pkg/internal/controller.(*Controller).reconcileHandler\n\tsigs.k8s.io/controller-runtime@v0.13.1/pkg/internal/controller/controller.go:320\nsigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).processNextWorkItem\n\tsig
s.k8s.io/controller-runtime@v0.13.1/pkg/internal/controller/controller.go:273\nsigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2.2\n\tsigs.k8s.io/controller-runtime@v0.13.1/pkg/internal/controller/controller.go
:234"}