story #7511: fetch the list of allowed tracker types for the top backlog

Change-Id: Ia9e947b38c5eb2b50d46e6033aebd0ca28af324e
Merge commit '1932bb2' into HEAD

* commit '1932bb2':
  story #7511: fetch the list of allowed tracker types for the top backlog

Change-Id: I86f375818ad1b48ccc26e789583b1b4da07d8611
 This is Tuleap 7.7.99.76

Change-Id: I6f2b13015fa4c133c76ab70a83dfa77cba5ddfa6