Add related_epic permissions

Adds permissions for reading and managing related epics. These will be
used similarly as issue_link permissions, but for epics. Also I added
these permissions to EpicPolicy instead of GroupPolicy as this
permission should be always called on a specific epic.

ee/app/models/license.rb

@@ -186,6 +186,7 @@ class License < ApplicationRecord
     prometheus_alerts
     pseudonymizer
     quality_management
+    related_epics
     release_evidence_test_artifacts
     report_approver_rules
     requirements

ee/app/policies/epic_policy.rb

@@ -10,6 +10,8 @@ class EpicPolicy < BasePolicy
     @subject.confidential?
   end
 
+  condition(:related_epics_available) { @subject.group.licensed_feature_available?(:related_epics) }
+
   rule { can?(:read_epic) }.policy do
     enable :read_epic_iid
     enable :read_note
@@ -40,4 +42,12 @@ class EpicPolicy < BasePolicy
     enable :set_epic_metadata
     enable :set_confidentiality
   end
+
+  rule { can?(:read_epic) & related_epics_available }.policy do
+    enable :read_related_epic_link
+  end
+
+  rule { can?(:admin_epic) & related_epics_available }.policy do
+    enable :admin_related_epic_link
+  end
 end

ee/spec/policies/epic_policy_spec.rb

@@ -27,22 +27,41 @@ RSpec.describe EpicPolicy do
   end
 
   shared_examples 'can only read epics' do
-    it do
-      is_expected.to be_allowed(:read_epic, :read_epic_iid, :read_note, :create_todo)
-      is_expected.to be_disallowed(:update_epic, :destroy_epic, :admin_epic, :create_epic)
+    it 'matches expected permissions' do
+      is_expected.to be_allowed(:read_epic, :read_epic_iid, :read_note,
+                                :create_todo, :read_related_epic_link)
+      is_expected.to be_disallowed(:update_epic, :destroy_epic, :admin_epic,
+                                   :create_epic, :admin_related_epic_link)
     end
   end
 
   shared_examples 'can manage epics' do
-    it { is_expected.to be_allowed(:read_epic, :read_epic_iid, :read_note, :update_epic, :admin_epic, :create_epic, :create_todo) }
+    it 'matches expected permissions' do
+      is_expected.to be_allowed(:read_epic, :read_epic_iid, :read_note,
+                                :update_epic, :admin_epic, :create_epic,
+                                :create_todo, :read_related_epic_link,
+                                :admin_related_epic_link)
+    end
   end
 
   shared_examples 'all epic permissions disabled' do
-    it { is_expected.to be_disallowed(:read_epic, :read_epic_iid, :update_epic, :destroy_epic, :admin_epic, :create_epic, :create_note, :award_emoji, :read_note, :create_todo) }
+    it 'matches expected permissions' do
+      is_expected.to be_disallowed(:read_epic, :read_epic_iid, :update_epic,
+                                   :destroy_epic, :admin_epic, :create_epic,
+                                   :create_note, :award_emoji, :read_note,
+                                   :create_todo, :read_related_epic_link,
+                                   :admin_related_epic_link)
+    end
   end
 
   shared_examples 'all reporter epic permissions enabled' do
-    it { is_expected.to be_allowed(:read_epic, :read_epic_iid, :update_epic, :admin_epic, :create_epic, :create_note, :award_emoji, :read_note, :create_todo) }
+    it 'matches expected permissions' do
+      is_expected.to be_allowed(:read_epic, :read_epic_iid, :update_epic,
+                                :admin_epic, :create_epic, :create_note,
+                                :award_emoji, :read_note, :create_todo,
+                                :read_related_epic_link,
+                                :admin_related_epic_link)
+    end
   end
 
   shared_examples 'group member permissions' do
@@ -111,7 +130,7 @@ RSpec.describe EpicPolicy do
 
   context 'when epics feature is enabled' do
     before do
-      stub_licensed_features(epics: true)
+      stub_licensed_features(epics: true, related_epics: true)
     end
 
     context 'when an epic is in a private group' do
@@ -227,5 +246,22 @@ RSpec.describe EpicPolicy do
         it_behaves_like 'all reporter epic permissions enabled'
       end
     end
+
+    context 'when related_epics feature is not available' do
+      let(:group) { create(:group) }
+
+      before do
+        stub_licensed_features(epics: true)
+        group.add_maintainer(user)
+      end
+
+      it 'matches expected permissions' do
+        is_expected.to be_allowed(:read_epic, :read_epic_iid, :update_epic,
+                                  :admin_epic, :create_epic, :create_note,
+                                  :award_emoji, :read_note, :create_todo)
+        is_expected.to be_disallowed(:read_related_epic_link,
+                                     :admin_related_epic_link)
+      end
+    end
   end
 end