Allow to access Container Registry for Public and Internal projects

What does this MR do?

Adds missing ability read_container_image for public scope which affects users accessing public and internal projects.

Why was this MR needed?

Previously, we allowed to use container registry for anonymous users, but did not allow to do the same for logged in. This MR makes it possible.

What are the relevant issue numbers?

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/18176 https://gitlab.com/gitlab-org/gitlab-ce/issues/19668 https://gitlab.com/gitlab-org/gitlab-ce/issues/19117

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together