Indexer works with smaller batches of repositories to not exceed NOFILE limit

CHANGELOG-EE

@@ -3,6 +3,7 @@ Please view this file on the master branch, on stable branches it's out of date.
 v 8.13.0 (unreleased)
 v 8.12.4 (unreleased)
+  - [ES] Indexer works with smaller batches of repositories to not exceed NOFILE limit
 v 8.12.3
   - Fix prevent_secrets checkbox on admin view
@@ -13,7 +14,7 @@ v 8.12.2
 v 8.12.1
   - Prevent secrets to be pushed to the repository
-- Prevent secrets to be pushed to the repository
+  - Prevent secrets to be pushed to the repository
 v 8.12.0
   - Include more data in EE usage ping

lib/tasks/gitlab/elastic.rake

@@ -23,7 +23,7 @@ namespace :gitlab do
       indexer = Gitlab::Elastic::Indexer.new
-      projects.find_each do |project|
+      projects.find_each(batch_size: 300) do |project|
         repository = project.repository
         if repository.exists? && !repository.empty?