This is step one of resolving
https://gitlab.com/gitlab-org/gitlab-ce/issues/56838.

Here is what changed:
- Revert the security fix from bdee9e84.
- Do not leak repository information (tag name, commit) to guests in API
responses.
- Do not include links to source code in API responses for users that do
not have download_code access.
- Show Releases in sidebar for guests.
- Do not display links to source code under Assets for users that do not
have download_code access.

GET ':id/releases/:tag_name' still do not allow guests to access
releases. This is to prevent guessing tag existence.