Add support in docker install method to auto-generate ci connection (behind a flag)

Add support in docker install method to auto-generate ci connection (behind a flag)

1. Add ability to copy ci connection from main connection. The ci connection will connect to the same database as the main connection
2. It will be behind a flag (that is suitable for docker install method). The flag will default to false. Customers can flip this to true if they wish to opt-in earlier than %16.0.

The intention is that this flag will flip to true in %16.0

Details

The docker images are hosted in https://hub.docker.com/r/gitlab/gitlab-ee/. It's built by omnibus-gitlab (https://gitlab.com/gitlab-org/omnibus-gitlab/-/blob/master/doc/build/index.md#all-in-one-docker-image); To be specific, tag and nightly pipelines of dev.gitlab.org/gitlab/omnibus-gitlab/ pushes them.

• https://docs.gitlab.com/ee/install/docker.html#configuration