Add system note for when paging starts on a manually created incident

Indicates the escalation policy which is being notified of the incident.
Behind feature flag :incident_escalations.

ee/app/helpers/ee/system_note_helper.rb

@@ -22,7 +22,8 @@ module EE
       'vulnerability_confirmed' => 'shield',
       'vulnerability_dismissed' => 'cancel',
       'vulnerability_resolved' => 'status_closed',
-      'published' => 'bullhorn'
+      'published' => 'bullhorn',
+      'paging_started' => 'mobile'
     }.freeze
 
     override :system_note_icon_name

ee/app/models/ee/system_note_metadata.rb

@@ -9,7 +9,7 @@ module EE
       epic_issue_added issue_added_to_epic epic_issue_removed issue_removed_from_epic
       epic_issue_moved issue_changed_epic epic_date_changed relate_epic unrelate_epic
       vulnerability_confirmed vulnerability_dismissed vulnerability_resolved vulnerability_detected
-      iteration
+      iteration paging_started
     ].freeze
 
     EE_TYPES_WITH_CROSS_REFERENCES = %w[

ee/app/services/ee/incident_management/issuable_escalation_statuses/after_update_service.rb

@@ -56,6 +56,7 @@ module EE
 
         def create_escalations
           ::IncidentManagement::PendingEscalations::IssueCreateWorker.perform_async(issuable.id)
+          ::SystemNoteService.start_escalation(issuable, escalation_status.policy, current_user)
         end
       end
     end

ee/app/services/ee/system_note_service.rb

@@ -116,6 +116,10 @@ module EE
       escalations_service(noteable, project).notify_via_escalation(recipients, escalation_policy: escalation_policy, type: type)
     end
 
+    def start_escalation(noteable, escalation_policy, author)
+      escalations_service(noteable, noteable.project).start_escalation(escalation_policy, author)
+    end
+
     private
 
     def issuables_service(noteable, project, author)

ee/app/services/system_notes/escalations_service.rb

@@ -13,5 +13,12 @@ module SystemNotes
 
       create_note(NoteSummary.new(noteable, project, author, body, action: 'new_alert_added'))
     end
+
+    def start_escalation(escalation_policy, author)
+      path = url_helpers.project_incident_management_escalation_policies_path(project)
+      body = "paged escalation policy [#{escalation_policy.name}](#{path})"
+
+      create_note(NoteSummary.new(noteable, project, author, body, action: 'paging_started'))
+    end
   end
 end

ee/spec/services/ee/incident_management/issuable_escalation_statuses/after_update_service_spec.rb

@@ -95,6 +95,7 @@ RSpec.describe IncidentManagement::IssuableEscalationStatuses::AfterUpdateServic
 
         if should_create
           expect(::IncidentManagement::PendingEscalations::IssueCreateWorker).to receive(:perform_async).with(issue.id)
+          expect(::SystemNoteService).to receive(:start_escalation).with(issue, escalation_policy, current_user)
         else
           expect(::IncidentManagement::PendingEscalations::IssueCreateWorker).not_to receive(:perform_async)
         end

ee/spec/services/system_note_service_spec.rb

@@ -161,4 +161,16 @@ RSpec.describe SystemNoteService do
       described_class.publish_issue_to_status_page(noteable, project, author)
     end
   end
+
+  describe '.start_escalation' do
+    let(:policy) { double(project: project) }
+
+    it 'calls EscalationsService' do
+      expect_next_instance_of(::SystemNotes::EscalationsService) do |service|
+        expect(service).to receive(:start_escalation).with(policy, author)
+      end
+
+      described_class.start_escalation(noteable, policy, author)
+    end
+  end
 end

ee/spec/services/system_notes/escalations_service_spec.rb

@@ -3,15 +3,17 @@
 require 'spec_helper'
 
 RSpec.describe SystemNotes::EscalationsService do
+  include Gitlab::Routing
+
   let_it_be(:project) { create(:project) }
   let_it_be(:user) { create(:user) }
   let_it_be(:user_2) { create(:user) }
   let_it_be(:author) { User.alert_bot }
+  let_it_be(:escalation_policy) { create(:incident_management_escalation_policy, project: project) }
 
   describe '#notify_via_escalation' do
     subject { described_class.new(noteable: noteable, project: project).notify_via_escalation([user, user_2], escalation_policy: escalation_policy, type: type) }
 
-    let_it_be(:escalation_policy) { create(:incident_management_escalation_policy, project: project) }
     let_it_be(:noteable) { create(:alert_management_alert, project: project) }
     let_it_be(:type) { :alert }
 
@@ -23,4 +25,23 @@ RSpec.describe SystemNotes::EscalationsService do
       expect(subject.note).to match("notified #{user.to_reference} and #{user_2.to_reference} of this #{type} via escalation policy **#{escalation_policy.name}**")
     end
   end
+
+  describe '#start_escalation' do
+    let_it_be(:noteable) { create(:issue, project: project) }
+    let_it_be(:author) { user }
+
+    subject do
+      described_class
+      .new(noteable: noteable, project: project)
+      .start_escalation(escalation_policy, user)
+    end
+
+    it_behaves_like 'a system note' do
+      let(:action) { 'paging_started' }
+    end
+
+    it 'posts the correct text to the system note' do
+      expect(subject.note).to match("paged escalation policy [#{escalation_policy.name}](#{project_incident_management_escalation_policies_path(project)})")
+    end
+  end
 end