Customise a format of notification mail

Is there any template file for notification emails( Text e-mail)?

I need to add a kind of footer to GitLab notification mail. I must use Text e-mails. not HTML emails.
I edit text.erb files in /opt/gitlab/embedded/service/gitlab-rails/app/views/notify/, then I can add footer. But there is 33 text.erb files.

In case of HTML emails, following file is exist.
/opt/gitlab/embedded/service/gitlab-rails/app/views/layouts/notify.html.haml

Thank you in advanced.