Support for external alerts in the New Kibana Alerting Experience

**What the feature is (as Title)**

Support for external alerts in New Kibana Alerting Experience.

**Value proposition**

Most organizations do not run on a single alerting tool. Datadog, Prometheus, cloud-native monitors, and other platforms still fire incidents that security and operations teams need to see in context with Elastic data. Today, those signals often live in separate consoles, making correlation, handoff, and unified response harder than it should be.

External alert support in the New Kibana Alerting Experience closes that gap without forcing a rip-and-replace. Teams can centralize triage in Kibana while keeping upstream systems in place, and apply the same investigation patterns, acknowledgement, assignment, workflows, and rules-on-rules correlation across both native and imported alerts. One alerts experience, regardless of the origin.

**Expected outcome**
The New Kibana Alerting Experience will let teams bring alerts from external monitoring and observability systems into Kibana alongside alerts generated by Kibana rules. External alerts are ingested into the same alerting model, so users can view, triage, and act on them in the alerts list and related workflows, the same way they do for native Kibana rule alerts.