story #7511: adding route PATCH /projects/:id/backlog

Change-Id: I8fad972b57fff16448ba0345629282b42bfe8d6c
Merge commit 'refs/changes/05/3305/3' of ssh://gerrit.tuleap.net:29418/tuleap into tuleap-stable-master

* ssh://gerrit.tuleap.net:29418/tuleap:
  story #7511: adding route PATCH /projects/:id/backlog

Change-Id: I6f4e5cb9de30a8373a445bb2e29c7d44a0440537
This is Tuleap 7.7.99.50

Change-Id: I5e60c0d43f1f6ff0b843fa54ff58b7a0c7fa288e