Enable Container Registry by default

When installing gitlab via omnibus package, it would be great to have Container Registry enabled by default. We can use custom port for that. For example if user set instance domain name to gitlab.example.com we can have registry running on gitlab.example.com:5050

Since we use LetsEncrypt and providing external url during setup is enough for us, I don't see why we can't do it automatically.

sudo EXTERNAL_URL="https://gitlab.example.com" apt-get install gitlab-ee

means we can easily put registry_external_url 'https://gitlab.example.me:5050' into /etc/gitlab/gitlab.rb config

Why we need this

For great user experience with AutoDevOps. Right now if I install GitLab and create new project with AutoDevOps pipeline, it fails on build stage because Container registry is disabled by default