Add ability to customize Auto-DevOps.gitlab-ci.yml for gitlab instance

Default Auto-DevOps.gitlab-ci.yml may sometimes be limiting to some use-cases and need to be extended on a per-instance level in cases when gitlab instance has many projects. Currently, the only way to do that is to bind-mount your own version of the gitlab ci template to /opt/gitlab/embedded/service/gitlab-rails/vendor/gitlab-ci-yml/Auto-DevOps.gitlab-ci.yml . This doesn't seem like a clean solution and would be nice to have an ability to be able to customize this template, so that we don't have to make some modifications in every single project.

thank you for consideration