Prefix notifications with '/'

Purposely didn't update other routes until we have consensus. Will
do so in a follow up

Bug: 58239
Change-Id: I937a2b88a74cee88d7a35aa0c90b95f37fdd5047
(cherry picked from commit d27526cc1e3d8717e7bfbbdb39ebe6cb34d4c41d)