Use gitlab_fingerprint in prometheus alert worker

`ProcessPrometheusAlertWorker` now uses `Alert#gitlab_fingerprint`
to find `PrometheusAlertEvent` and `SelfManagedPrometheusAlertEvent`
records

app/workers/incident_management/process_prometheus_alert_worker.rb

@@ -41,23 +41,11 @@ module IncidentManagement
     end
 
     def find_gitlab_managed_event(alert)
-      payload_key = payload_key_for_alert(alert)
-
-      PrometheusAlertEvent.find_by_payload_key(payload_key)
+      PrometheusAlertEvent.find_by_payload_key(alert.gitlab_fingerprint)
     end
 
     def find_self_managed_event(alert)
-      payload_key = payload_key_for_alert(alert)
-
-      SelfManagedPrometheusAlertEvent.find_by_payload_key(payload_key)
-    end
-
-    def payload_key_for_alert(alert)
-      if alert.gitlab_managed?
-        PrometheusAlertEvent.payload_key_for(alert.metric_id, alert.starts_at_raw)
-      else
-        SelfManagedPrometheusAlertEvent.payload_key_for(alert.starts_at_raw, alert.title, alert.full_query)
-      end
+      SelfManagedPrometheusAlertEvent.find_by_payload_key(alert.gitlab_fingerprint)
     end
 
     def create_issue(project, alert)

spec/workers/incident_management/process_prometheus_alert_worker_spec.rb

@@ -6,7 +6,7 @@ describe IncidentManagement::ProcessPrometheusAlertWorker do
   describe '#perform' do
     let_it_be(:project) { create(:project) }
     let_it_be(:prometheus_alert) { create(:prometheus_alert, project: project) }
-    let_it_be(:payload_key) { PrometheusAlertEvent.payload_key_for(prometheus_alert.prometheus_metric_id, prometheus_alert.created_at.rfc3339) }
+    let(:payload_key) { Gitlab::Alerting::Alert.new(project: project, payload: alert_params).gitlab_fingerprint }
     let!(:prometheus_alert_event) { create(:prometheus_alert_event, prometheus_alert: prometheus_alert, payload_key: payload_key) }
 
     let(:alert_params) do
@@ -107,7 +107,6 @@ describe IncidentManagement::ProcessPrometheusAlertWorker do
       let(:starts_at) { Time.now.rfc3339 }
 
       let!(:prometheus_alert_event) do
-        payload_key = SelfManagedPrometheusAlertEvent.payload_key_for(starts_at, alert_name, 'vector(1)')
         create(:self_managed_prometheus_alert_event, project: project, payload_key: payload_key)
       end