Validate project key presence if Jira issues enabled

As part of the Jira issues integration
https://gitlab.com/groups/gitlab-org/-/epics/3622 we need to validate
the presence of the project key when enabling the Jira issues.

app/models/project_services/jira_service.rb

@@ -440,3 +440,5 @@ class JiraService < IssueTrackerService
     end
   end
 end
+
+JiraService.prepend_if_ee('EE::JiraService')

ee/app/models/project_services/ee/jira_service.rb

+# frozen_string_literal: true
+
+module EE
+  module JiraService
+    extend ActiveSupport::Concern
+
+    prepended do
+      validates :project_key, presence: true, if: :issues_enabled
+    end
+  end
+end

ee/spec/features/integrations/jira/jira_issues_list_spec.rb

@@ -4,7 +4,7 @@ require 'spec_helper'
 
 RSpec.describe 'Jira issues list' do
   let_it_be(:project, refind: true) { create(:project) }
-  let_it_be(:jira_integration) { create(:jira_service, project: project, issues_enabled: true) }
+  let_it_be(:jira_integration) { create(:jira_service, project: project, issues_enabled: true, project_key: 'GL') }
   let(:user) { create(:user) }
 
   before do

ee/spec/models/project_services/jira_service_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe JiraService do
+  let(:jira_service) { build(:jira_service) }
+
+  describe 'validations' do
+    it 'validates presence of project_key if issues_enabled' do
+      jira_service.project_key = ''
+      jira_service.issues_enabled = true
+
+      expect(jira_service).to be_invalid
+    end
+  end
+end

spec/factories/services.rb

@@ -77,13 +77,16 @@ FactoryBot.define do
       username { 'jira_username' }
       password { 'jira_password' }
       jira_issue_transition_id { '56-1' }
+      issues_enabled { false }
+      project_key { nil }
     end
 
     after(:build) do |service, evaluator|
       if evaluator.create_data
         create(:jira_tracker_data, service: service,
                url: evaluator.url, api_url: evaluator.api_url, jira_issue_transition_id: evaluator.jira_issue_transition_id,
-               username: evaluator.username, password: evaluator.password
+               username: evaluator.username, password: evaluator.password, issues_enabled: evaluator.issues_enabled,
+               project_key: evaluator.project_key
         )
       end
     end