Update Dependency Proxy to default to on at the group level
Problem to solve
With %11.11 we launched the MVC of the dependency proxy for containers. Although the feature defaults to 'on' at the instance level, the default is 'off' at the group level. We did this, because we did not make a decision about if we should set the default configuration to docker hub or to quay.io.
We need to decide on a default setting (docker hub or quay.io) and make a decision. This is in line with GitLab's convention over configuration policy. We can always change the default container registry or improve the UI for updating it, but in order to drive usage we should set the default to on.
Software developers that are using the Container Registry and relying on it to download their blobs and images. Setting the default to on, will allow those users to take advantage of the proxy without having to configure anything.