Add UI docs for threat monitoring policy alerts

- add new screenshots

doc/user/application_security/threat_monitoring/index.md

@@ -159,7 +159,53 @@ Rule mode supports the following rule types:
 - [Level 4](https://docs.cilium.io/en/v1.8/policy/language/#layer-4-examples)
   can be added to all other rules.
 
+### Configureing Policy Alerts
+
+> [Introduced](https://gitlab.com/groups/gitlab-org/-/epics/3438) in [GitLab Ultimate](https://about.gitlab.com/pricing/) 13.9.
+
+The policy alert allows you to track what impact your policy is having. It can be enabled in the Policy Editor UI or with YAML using the `metadata.annotations` property.
+
+![Policy Editor UI](img/threat_monitoring_add_policy_alert_ui_v13_9.png)
+
+```yaml
+metadata:
+  annotations:
+    app.gitlab.com/alert: 'true'
+```
+
+Once added the UI will update with a warning about the dangers of too many alerts.
+
+![Alert Configured UI](img/threat_monitoring_policy_alert_configured_ui_v13_9.png)
+
+If you have not [configured the agent](../../project/clusters/protect/container_network_security/quick_start_guide.md), alerts will not be available to you and will guide you to the appropriate documentation ([install](../../clusters/agent/repository.md), [configure a Kubernetes Agent for this project](../../clusters/agent/index.md#create-an-agent-record-in-gitlab))
+
+![Policy Alerts Not Available ](img/threat_monitoring_policy_alerts_unavailable_v13_9.png)
+
 Once your policy is complete, save it by pressing the **Save policy**
 button at the bottom of the editor. Existing policies can also be
 removed from the editor interface by clicking the **Delete policy**
 button at the bottom of the editor.
+
+To view your alerts, view the alert list
+
+### Container Network Policy Alert list
+
+> [Introduced](https://gitlab.com/groups/gitlab-org/-/epics/3438) in [GitLab Ultimate](https://about.gitlab.com/pricing/) 13.9.
+
+The policy alert list allows you to view the policy activity. Alerts can be sorgedd by date/time and status.
+
+![Policy Alert List](img/threat_monitoring_policy_alert_list_v13_9.png)
+
+Policy alert statuses can be updaded to reflect that the alert has been seen and dealt with
+
+![Policy Alert Status](img/threat_monitoring_policy_alert_status_v13_9.png)
+
+By default the list filters out any resolved/dismissed alerts, but toggled on/off
+
+![Policy Alert Status Filter](img/threat_monitoring_hide_resolved_policy_alerts_v13_9.png)
+
+By default, the policy alerts are not enabled, so the policy alert list will guide you this documentation to enable it
+
+![Policy Alerts Disabled](img/threat_monitoring_policy_alerts_disabled_v13_9.png)
+
+> [Additional work](https://gitlab.com/groups/gitlab-org/-/epics/5041) coming in [GitLab Ultimate](https://about.gitlab.com/pricing/).