WIP: Using a dependency proxy

What does this MR do?

Creates a group which is used as a dependency proxy. By doing this, it is possible with a docker pull command to pull the image through the new proxy and thus save the image on the gitlab instance. For this, docker needs to have and insecure repository setting added. After this a pull from a non https source can be done.

This MR closes gitlab-org/quality/testcases#222 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Style guides
• Separation of EE specific content