tasks #7480: be able to add a new git mirror

Change-Id: Iad04260d3527653833f16cd5191af97d525b34f5
Merge commit 'refs/changes/50/3050/12' of ssh://gerrit.tuleap.net:29418/tuleap into stable

* ssh://gerrit.tuleap.net:29418/tuleap:
  tasks #7480: be able to add a new git mirror
This is Tuleap 7.5.99.29

Change-Id: I1c987520615ed06fd9c9d422f3b0782689fc075b