ES: Fix monkey patch not loaded

GemExtensions::Elasticsearch::Model::Indexing::InstanceMethods is no
longer prepended to the proxies, thus the project’s _id is
incorrectly being set as “1” instead of “project_1". This means
joining would fail.

In the past, in config/initializers/elastic_client_setup.rb:

1. ES::Model::Indexing::InstanceMethods is included in
ES::Model::Proxy::InstanceMethodsProxy

2. Our monkey-patch is then prepended to
Elasticsearch::Model::Indexing::InstanceMethods

Since prepending happens later, our monkey patch would not be part of
ES::Model::Proxy::InstanceMethodsProxy's ancestor.

However it did work, by luck, because ES::Git::Model would
later include ES::Model, which would trigger the second
`include` call, and in turn add prepend modules into the ancestors.

But in previous commit, Elasticsearch::Git::Model is removed,
therefore the monkey patch was no longer included.

config/initializers/elastic_client_setup.rb

@@ -7,6 +7,17 @@ require 'gitlab/current_settings'
 Gitlab.ee do
   require 'elasticsearch/model'
 
+  ### Monkey patches
+
+  Elasticsearch::Model::Response::Records.prepend GemExtensions::Elasticsearch::Model::Response::Records
+  Elasticsearch::Model::Adapter::Multiple::Records.prepend GemExtensions::Elasticsearch::Model::Adapter::Multiple::Records
+  Elasticsearch::Model::Indexing::InstanceMethods.prepend GemExtensions::Elasticsearch::Model::Indexing::InstanceMethods
+  Elasticsearch::Model::Adapter::ActiveRecord::Importing.prepend GemExtensions::Elasticsearch::Model::Adapter::ActiveRecord::Importing
+  Elasticsearch::Model::Client::InstanceMethods.prepend GemExtensions::Elasticsearch::Model::Client
+  Elasticsearch::Model::Client::ClassMethods.prepend GemExtensions::Elasticsearch::Model::Client
+  Elasticsearch::Model::ClassMethods.prepend GemExtensions::Elasticsearch::Model::Client
+  Elasticsearch::Model.singleton_class.prepend GemExtensions::Elasticsearch::Model::Client
+
   ### Modified from elasticsearch-model/lib/elasticsearch/model.rb
 
   [
@@ -32,15 +43,4 @@ Gitlab.ee do
       target.respond_to?(:as_indexed_json) ? target.__send__(:as_indexed_json, options) : super
     end
   CODE
-
-  ### Monkey patches
-
-  Elasticsearch::Model::Response::Records.prepend GemExtensions::Elasticsearch::Model::Response::Records
-  Elasticsearch::Model::Adapter::Multiple::Records.prepend GemExtensions::Elasticsearch::Model::Adapter::Multiple::Records
-  Elasticsearch::Model::Indexing::InstanceMethods.prepend GemExtensions::Elasticsearch::Model::Indexing::InstanceMethods
-  Elasticsearch::Model::Adapter::ActiveRecord::Importing.prepend GemExtensions::Elasticsearch::Model::Adapter::ActiveRecord::Importing
-  Elasticsearch::Model::Client::InstanceMethods.prepend GemExtensions::Elasticsearch::Model::Client
-  Elasticsearch::Model::Client::ClassMethods.prepend GemExtensions::Elasticsearch::Model::Client
-  Elasticsearch::Model::ClassMethods.prepend GemExtensions::Elasticsearch::Model::Client
-  Elasticsearch::Model.singleton_class.prepend GemExtensions::Elasticsearch::Model::Client
 end

ee/spec/lib/gem_extensions/elasticsearch/model/indexing/instance_methods_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe GemExtensions::Elasticsearch::Model::Indexing::InstanceMethods do
+  describe '#index_document' do
+    let(:project) { Project.new(id: 1) }
+
+    it 'overrides _id with type being prepended' do
+      proxy = Elastic::Latest::ProjectInstanceProxy.new(project)
+
+      expect(proxy.client).to receive(:index).with(
+        index: 'gitlab-test',
+        type: 'doc',
+        id: 'project_1',
+        body: proxy.as_indexed_json
+      )
+
+      proxy.index_document
+    end
+  end
+end