Disable epic quick actions for not persisted epics

Adding/removal of epic links expects that both parent and child epics
are created. If parent_epic is applied on a new not-persisted epic,
then EpicLink then this epic link is created before target epic is saved
which has couple of side-effects:
* CreateService's set_child_epic fails to update the new epic
* no system notes are created
* internal_id for epics is out-of-sync because EpicLink attempts to
  store new epic (and fails and rolls-back thsi save) -> then
  internal_id is already set which target epic is saved (as part of
  regular save operation) but not bumped in DB

Because epic quick actions don't work properly with unpersisted epics,
it will be disabled until the code is updated to work properly with new
epics.

Also DB migration to reset internal_id is renamed to re-enqueue (and
re-run) it again.

db/migrate/20201202081429_update_internal_ids_last_value_for_epics.rb → db/migrate/20201208081429_update_internal_ids_last_value_for_epics_renamed.rb

 # frozen_string_literal: true
 
-class UpdateInternalIdsLastValueForEpics < ActiveRecord::Migration[6.0]
+class UpdateInternalIdsLastValueForEpicsRenamed < ActiveRecord::Migration[6.0]
   DOWNTIME = false
 
   def up

db/schema_migrations/20201202081429

-cbc6bfa122167e9a46edaa14351a73eeb10586fa0eb82f231c792384c9d7986c
\ No newline at end of file

db/schema_migrations/20201208081429

+5c429e8090fd779ba29a8bd78d69e78d1d5d143a6fd3097a715e178fb150d877
\ No newline at end of file

ee/changelogs/unreleased/epic_iid_fix.yml

+---
+title: Disable epic quick actions when creating new epics
+merge_request: 49470
+author:
+type: fixed

ee/lib/ee/gitlab/quick_actions/epic_actions.rb

@@ -90,6 +90,7 @@ module EE
           end
 
           def action_allowed?
+            quick_action_target.persisted? &&
               quick_action_target.group&.feature_available?(:subepics) &&
               current_user.can?(:"admin_#{quick_action_target.to_ability_name}", quick_action_target)
           end

ee/spec/services/quick_actions/interpret_service_spec.rb

@@ -503,6 +503,12 @@ RSpec.describe QuickActions::InterpretService do
             let(:target) { merge_request }
           end
 
+          context 'when target epic is not persisted yet' do
+            let(:target) { build(:epic, group: group) }
+
+            it_behaves_like 'quick action is unavailable', :child_epic
+          end
+
           context 'when passed child epic is nil' do
             let(:child_epic) { nil }
 
@@ -647,6 +653,12 @@ RSpec.describe QuickActions::InterpretService do
             let(:target) { merge_request }
           end
 
+          context 'when target epic is not persisted yet' do
+            let(:target) { build(:epic, group: group) }
+
+            it_behaves_like 'quick action is unavailable', :remove_child_epic
+          end
+
           it_behaves_like 'epic relation is removed'
 
           context 'when trying to remove child epic from a different epic' do
@@ -1176,6 +1188,12 @@ RSpec.describe QuickActions::InterpretService do
           it_behaves_like 'target epic does not exist', :parent
         end
 
+        context 'when target epic is not persisted yet' do
+          let(:target) { build(:epic, group: group) }
+
+          it_behaves_like 'quick action is unavailable', :parent_epic
+        end
+
         context 'when user has no permission to read epic' do
           let(:content) { "/parent_epic #{epic2&.to_reference(epic)}" }
 
@@ -1209,6 +1227,12 @@ RSpec.describe QuickActions::InterpretService do
           end
         end
 
+        context 'when target epic is not persisted yet' do
+          let(:target) { build(:epic, group: group) }
+
+          it_behaves_like 'quick action is unavailable', :remove_parent_epic
+        end
+
         context 'when parent is not present' do
           before do
             epic.parent = nil

spec/migrations/update_internal_ids_last_value_for_epics_spec.rb → spec/migrations/update_internal_ids_last_value_for_epics_renamed_spec.rb

 # frozen_string_literal: true
 
 require 'spec_helper'
-require Rails.root.join('db', 'migrate', '20201202081429_update_internal_ids_last_value_for_epics.rb')
+require Rails.root.join('db', 'migrate', '20201208081429_update_internal_ids_last_value_for_epics_renamed.rb')
 
-RSpec.describe UpdateInternalIdsLastValueForEpics, :migration, schema: 20201124185639 do
+RSpec.describe UpdateInternalIdsLastValueForEpicsRenamed, :migration, schema: 20201124185639 do
   let(:namespaces) { table(:namespaces) }
   let(:users) { table(:users) }
   let(:epics) { table(:epics) }