Permanent link to latest version of a release

Description

Related to/ Extended from : #22273 (closed)

Now that we have the GitLab Releases feature (https://gitlab.com/gitlab-org/gitlab-ce/issues/41766), we should make sure that it is as easy to use as possible. Retrieving a link to source or an asset should be possible using a predictable URL. Something like /releases/11.4/source.tar.gz, releases/11.4/installer.dmg, and so on. In the interest of making this easy to use, we should also support a way to point to latest:

In this example, /releases/latest/installer.dmg could substitute latest with 11.4. We may need some kind of syntax to differentiate the latest tag from a release that's unfortunately named "latest."

Proposal

Because internally these are all links, it should be possible to handle all of this through redirects. I.e., if the URL for installer.dmg is http://download.com/myrelease/11.4/installer.dmg, visiting /releases/11.4/installer.dmg should result in a redirect to the internal or external site (we should show a heads up message if we are redirecting to an external site). Similarly, visiting latest, if latest is 11.4, we can follow the redirects to get to the right asset eventually.

Use-case

Suppose I use GitLab.com to host my software project and uses GItLab CI to build the software. I could easily link to the latest version of the software from my website, without having to edit the website each time I push a new version to modify the link.