SpecialRedirect: Add @since documentation and add release notes

The Special:Redirect page was added in change
I8b0785f4fbdb3dd438a7a45263c5f375ff9d2208.

Change-Id: I1a4b9a8b0a008f16e554f7edc2f21b7142fde8d4
Merge "SpecialRedirect: Add @since documentation and add release notes"