Add cop to deprecate Database.bulk_insert

See https://gitlab.com/gitlab-org/gitlab/-/issues/207989

rubocop/cop/gitlab/bulk_insert.rb

+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Gitlab
+      # Cop that disallows the use of `Gitlab::Database.bulk_insert`, in favour of using
+      # the `BulkInsertSafe` module.
+      class BulkInsert < RuboCop::Cop::Cop
+        MSG = 'Use the `BulkInsertSafe` concern, instead of using `Gitlab::Database.bulk_insert`. See https://docs.gitlab.com/ee/development/insert_into_tables_in_batches.html'
+
+        def_node_matcher :raw_union?, <<~PATTERN
+          (send (const (const nil? :Gitlab) :Database) :bulk_insert ...)
+        PATTERN
+
+        def on_send(node)
+          return unless raw_union?(node)
+
+          add_offense(node, location: :expression)
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/gitlab/bulk_insert_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require 'rubocop'
+require 'rubocop/rspec/support'
+require_relative '../../../../rubocop/cop/gitlab/bulk_insert'
+
+describe RuboCop::Cop::Gitlab::BulkInsert do
+  include CopHelper
+
+  subject(:cop) { described_class.new }
+
+  it 'flags the use of Gitlab::Database.bulk_insert' do
+    expect_offense(<<~SOURCE)
+    Gitlab::Database.bulk_insert('merge_request_diff_files', rows)
+    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use the `BulkInsertSafe` concern, instead of using `Gitlab::Database.bulk_insert`. See https://docs.gitlab.com/ee/development/insert_into_tables_in_batches.html
+    SOURCE
+  end
+end