Allow repo owner/admin to set raw links as publicly accessible
### Problem to solve
Repo owner doesn't want people to be able to look at his repo, but wants people to be able to download the file(s) they link to.
### Further details
Currently, setting the files to "Members only", even on a public repo, prevents users from downloading files from the repo using the raw links, unless they're members of such projects, and logged in.
### Proposal
Add a switch to the permission settings, labeled "Enable public raw links" or similar. With that switch, anyone with a link to a file in the repo would be able to download said file, without them being logged in, or having access to the rest of the repo.
### What does success look like, and how can we measure that?
Access private repo over a raw link with public raw links enabled should download the file that has been linked to.
### Links / references
issue