Make `internal` projects readible by all tokens / deploy keys

Project tokens are project-specific and currently have no access to any other projects. There's even an issue that deploy keys don't even have access to public projects (gitlab-foss#1217 (closed)).

Project tokens and deploy keys should have read-only access to public and internal projects, including for git submodules and container registry images.

This will have security implications, but my gut feeling is that read-only access to internal projects makes sense.