Rename rack_attack_new.rb back to rack_attack.rb

RackAttack config file was renamed to rack_attack_new.rb to make it compatible with Omnibus Settings gitlab-foss!31246 (comment 215110463).

Omnibus RackAttack settings were removed on %13.0, so we can rename the GitLab config file back to rack_attack.rb #29952 (closed)

Development log

• A merge request was created to rename the file and update the documentation !33072 (merged)
• Renaming the initializer caused a problem on GitLab QA mirror pipelines #219184 (closed)
  • Since the file was populated and simlinked by Omnibus, it tried to delete it after that but it no longer existed. Since the file is no longer managed by Omnibus, this is no longer necessary. #219184 (comment 349706338).
  • This was fixed on omnibus-gitlab!4269 (merged)
• An upgrade note was added for 13.0.1 to notify about the possibility of rack_attack.rb being overridden silently !33978 (merged)