Remove N+1 DB queries from indexing projects in Elasticsearch

The `#as_indexed_json` method is used to convert individual documents to
the JSON that is sent to Elasticsearch during indexing. We need to
preload the data before it gets to this method. We implemented the
`.preload_indexing_data` method in
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/56808 so we just
need to add this to the various classes now. This MR updates it for
`Project` only.

ee/changelogs/unreleased/324745-preload-projects-for-elasticsearch-indexing.yml

+---
+title: Remove N+1 DB queries from indexing projects in Elasticsearch
+merge_request: 57794
+author:
+type: performance

ee/lib/elastic/latest/project_class_proxy.rb

@@ -49,6 +49,12 @@ module Elastic
 
         search(query_hash, options)
       end
+
+      # rubocop: disable CodeReuse/ActiveRecord
+      def preload_indexing_data(relation)
+        relation.includes(:project_feature, :route)
+      end
+      # rubocop: enable CodeReuse/ActiveRecord
     end
   end
 end

ee/spec/services/elastic/process_bookkeeping_service_spec.rb

@@ -209,6 +209,20 @@ RSpec.describe Elastic::ProcessBookkeepingService, :clean_gitlab_redis_shared_st
     end
 
     context 'N+1 queries' do
+      it 'does not have N+1 queries for projects' do
+        projects = create_list(:project, 2)
+
+        described_class.track!(*projects)
+
+        control = ActiveRecord::QueryRecorder.new(skip_cached: false) { described_class.new.execute }
+
+        projects += create_list(:project, 3)
+
+        described_class.track!(*projects)
+
+        expect { described_class.new.execute }.not_to exceed_all_query_limit(control)
+      end
+
       it 'does not have N+1 queries for notes' do
         notes = []